feat(style): Introduce Prettier for automated code style enforcement

[pgfeller]

Summary

Resolves #334

Introduces Prettier as the automated code style formatter for this repository, along with pre-commit enforcement via Husky and lint-staged.

Changes

Tooling setup

• .prettierrc — Prettier configuration: printWidth=120, tabWidth=4, singleQuote, semi=false, trailingComma: es5, LF line endings
• .prettierignore — Excludes build outputs, node_modules, coverage reports, and generated/vendored files (openhab.tmLanguage.json, openhab-icon-theme.json)
• .husky/pre-commit — Pre-commit hook that runs lint-staged
• lint-staged config in package.json — runs prettier --write + eslint on staged TS/JS files; prettier --write on JSON/MD files
• eslint-config-prettier — disables ESLint formatting rules that conflict with Prettier
• New npm scripts: format, format:check, lint:fix

Formatter applied to existing files

All existing source files have been reformatted to bring the codebase into compliance with the new style rules.

Testing

The pre-commit hook was verified locally. All existing tests continue to pass (formatting-only changes, no logic affected).

Notes

• Linting (eslint rule improvements) will be handled separately as mentioned in Introduce automated code style enforcement #334.
• The Prettier config follows industry-standard defaults adjusted for this project's existing conventions (4-space indent, single quotes, no semicolons).

[Copilot]

Pull request overview

This PR introduces automated code formatting via Prettier (with pre-commit enforcement through Husky + lint-staged) and applies the formatter across the existing codebase to standardize style and reduce formatting-only review noise.

Changes:

• Add Prettier configuration/ignore rules plus Husky + lint-staged pre-commit enforcement and formatting/lint scripts.
• Reformat TS/JS/JSON/MD/CSS and workflow/config files to match the new style (4-space indent, single quotes, no semicolons, etc.).
• Add CI jobs to check formatting and run ESLint.

Reviewed changes

Copilot reviewed 76 out of 97 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tsconfig.json	Reformats TS project config to match Prettier JSON style.
snippets/openhab_sitemaps.json	Reformats snippet JSON.
snippets/openhab_rules_typeconversions.json	Reformats snippet JSON.
snippets/openhab_rules_designpattern.json	Reformats snippet JSON.
snippets/openhab_rules.json	Reformats snippet JSON (incl. whitespace cleanup).
snippets/openhab.json	Normalizes line endings/formatting for snippet JSON.
shared.webpack.config.js	Reformats shared webpack config to Prettier style.
serverJS/webpack.config.js	Reformats server webpack config to Prettier style.
serverJS/src/Server.js	Reformats language server implementation to Prettier style.
serverJS/src/LSPServer.js	Reformats module export object (comma/trailing style).
serverJS/src/ItemCompletion/ItemCompletionProvider.js	Reformats provider implementation; no intentional logic changes.
serverJS/src/ItemCompletion/Item.js	Reformats Item model implementation.
serverJS/src/DocumentValidation/DocumentValidator.js	Reformats validator module export formatting.
serverJS/package.json	Reformats package metadata JSON.
serverJS/jest-unit.json	Reformats Jest unit config JSON.
serverJS/jest-integration.json	Reformats Jest integration config JSON.
serverJS/tests/unit/Server.test.js	Reformats unit tests.
serverJS/tests/unit/LSPServer.test.js	Reformats unit tests.
serverJS/tests/unit/ItemCompletion/Item.test.js	Reformats unit tests.
serverJS/tests/unit/DocumentValidation/DocumentValidator.test.js	Reformats unit tests.
serverJS/tests/integration/Server.test.js	Reformats integration tests.
serverJS/tests/integration/LSPServer.test.js	Reformats integration tests.
serverJS/tests/integration/ItemCompletion/ItemCompletionProvider.test.js	Reformats integration tests.
serverJS/mocks/vscode-languageserver.js	Reformats Jest mock module.
serverJS/mocks/Server.js	Reformats Jest mock module.
serverJS/mocks/ItemCompletion/ItemCompletionProvider.js	Reformats Jest mock module.
serverJS/mocks/DocumentValidation/DocumentValidator.js	Reformats Jest mock module.
scripts/dev-help.js	Reformats dev helper script output concatenation.
package.json	Adds format/lint scripts, Husky/lint-staged/Prettier deps, lint-staged config, and view icons.
meta/language-configuration.json	Reformats language configuration JSON.
docs/USAGE.md	Reformats markdown (quotes/emphasis/escaping) to Prettier style.
client/webpack.config.js	Reformats client webpack config.
client/tsconfig.test.json	Reformats test TS config.
client/tsconfig.json	Reformats client TS config.
client/src/extension.ts	Reformats extension activation/commands wiring.
client/src/WebViews/media/vscode.css	Reformats CSS to consistent indentation/quoting.
client/src/WebViews/media/updateNoticePanel.css	Reformats CSS, including expanded selector formatting.
client/src/WebViews/media/reset.css	Reformats CSS reset file.
client/src/WebViews/getNonce.ts	Reformats nonce helper code style.
client/src/WebViews/UpdateNoticePanel.ts	Reformats Update Notice webview panel code.
client/src/WebViews/PreviewPanel.ts	Reformats preview webview panel code.
client/src/Utils/types.ts	Reformats exported constants/objects.
client/src/Utils/Utils.ts	Reformats utility functions and promise chains.
client/src/Utils/MigrationManager.ts	Reformats migration helper logic.
client/src/Utils/ConfigManager.ts	Reformats config manager implementation and event handler formatting.
client/src/ThingsExplorer/ThingsModel.ts	Reformats model code and fetch promise chain formatting.
client/src/ThingsExplorer/ThingsExplorer.ts	Reformats explorer tree provider.
client/src/ThingsExplorer/Thing.ts	Reformats Thing wrapper class.
client/src/ThingsExplorer/ItemsProvider.ts	Reformats snippet generation helpers/providers.
client/src/ThingsExplorer/IThing.ts	Reformats TS interface declaration.
client/src/ThingsExplorer/IChannel.ts	Reformats TS interface declaration.
client/src/ThingsExplorer/Channel.ts	Reformats Channel wrapper class.
client/src/LanguageClient/RemoteLanguageClientProvider.ts	Reformats remote LSP client provider.
client/src/LanguageClient/LocalLanguageClientProvider.ts	Reformats local LSP client provider.
client/src/ItemsExplorer/SitemapPartialProvider.ts	Reformats sitemap snippet provider.
client/src/ItemsExplorer/RuleProvider.ts	Reformats rule snippet provider.
client/src/ItemsExplorer/ItemsModel.ts	Reformats REST-backed items model.
client/src/ItemsExplorer/ItemsExplorer.ts	Reformats items tree provider.
client/src/ItemsExplorer/ItemsCompletion.ts	Reformats completion provider.
client/src/ItemsExplorer/Item.ts	Reformats Item wrapper class.
client/src/ItemsExplorer/IItem.ts	Reformats TS interface declaration.
client/src/HoverProvider/HoverProvider.ts	Reformats hover provider logic and promise chains.
client/package.json	Reformats client package JSON.
client/jest.config.js	Reformats Jest config JS object formatting.
client/tests/tsconfig.json	Reformats test TS config JSON.
client/tests/Utils.test.ts	Reformats client unit tests.
client/tests/ThingsModel.test.ts	Reformats client unit tests.
client/tests/ThingsExplorer.test.ts	Reformats client unit tests.
client/tests/ItemsModel.test.ts	Reformats client unit tests.
client/tests/ItemsExplorer.test.ts	Reformats client unit tests.
client/tests/HoverProvider.test.ts	Reformats client unit tests.
client/tests/ConfigManager.test.ts	Reformats client unit tests.
client/mocks/vscode.ts	Reformats VS Code API mock.
client/mocks/tsconfig.json	Reformats mock TS config JSON.
client/mocks/ascii-table.ts	Reformats mock module formatting.
README.md	Reformats markdown and reference definitions.
CHANGELOG.md	Normalizes line endings and formatting.
.vscode/tasks.json	Reformats VS Code tasks JSON.
.vscode/settings.json	Adds Prettier default formatter + format-on-save and reformats settings JSON.
.vscode/launch.json	Reformats VS Code launch configurations.
.vscode/extensions.json	Updates/reorders recommended extensions and reformats JSON.
.volta.json	Reformats Volta config JSON.
.prettierrc	Adds Prettier configuration.
.prettierignore	Adds Prettier ignore rules for generated/build outputs and vendored files.
.markdownlint.json	Minor formatting normalization.
.husky/pre-commit	Adds pre-commit hook to run lint-staged.
.github/workflows/stale.yml	Reformats workflow YAML indentation.
.github/workflows/ci.yml	Reformats CI YAML and adds format + lint jobs.
.github/hooks/block-github-browser.json	Reformats JSON hook configuration.
.github/ISSUE_TEMPLATE/feature_request.md	Reformats markdown template spacing.
.github/ISSUE_TEMPLATE/bug_report.md	Reformats markdown template spacing/lists.
.eslintrc.cjs	Reformats ESLint config to match Prettier style.

[pgfeller]

@copilot apply changes based on this feedback