Feat: Add Function Edit Page with TreeView file browser and CodeEditor.

[twoGiants]

Changes

• 🎁 Add Function Edit Page with TreeView file browser and SDK CodeEditor for editing function source code
• 🎁 FileTreeView component with loading state, empty state, dirty indicators, and directories-before-files sorting
• 🎁 Add fetch() and updateRepo() to SourceControlService for full repo tree retrieval and pushing changes
• 🎁 updateRepo caches commit SHA locally to handle GitHub's eventually consistent ref storage on rapid saves
• 🎁 Success alert after save with auto-dismiss, unsaved changes confirmation modal on navigation
• 🎁 Auto-select handler file based on runtime from func.yaml
• 🎁 Empty state with code icon when no file is selected
• 🧹 Migrate test runner from Jest to Vitest with MSW 2.x for GitHub API mocking
• 🧹 Merge RepoInfo and SourceRepo into single RepoMetadata type
• 🧹 Extract parseNamespaceAndRuntime, getLanguageFromPath, handlerMap into shared utils
• 🧹 Add CSP connect-src for GitHub API in dev mode (start-console.sh)
• 🧹 Add CSS, co-location, and React performance rules to style guide and architecture docs
• 🧹 Add draft PR step and communication rules to workflow docs

[matejvasek]

2. atob corrupts non-ASCII content (GithubService.ts, fetch method)
   atob(file.content) decodes base64 to a Latin-1 string. Any UTF-8 multi-byte characters (accented letters, CJK, emoji) in source files will be silently corrupted. The browser-correct approach is: new TextDecoder().decode(Uint8Array.from(atob(file.content), c => c.charCodeAt(0)))

I can confirm that unicode does not work "šč" results in "Å¡Ä�".