feat(#709): validate plugin config with manifest zod schema

[rbalogic]

Proposed Changes

Fixes #709

• Schema Support: Add optional configSchema support to the shared plugin manifest types so plugins can declare a Zod schema for their config.
• Validation: Validate plugins.<id>.config during plugin loading in the runner, before setup(), scrape(), or aggregate() are called.
• Context Injection: Pass the parsed Zod result into ctx.config, so plugins receive validated and transformed config values instead of raw YAML input.
• Testing: Extend loader and runner tests to cover manifest validation, successful config parsing, and fail-fast behavior for invalid plugin config.
• Documentation & Scaffolding: Update plugin scaffolding and plugin docs to show how to declare and use configSchema, including the required zod dependency.

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Merge Checklist

• Add specs that demonstrate the bug or test the new feature.
• Update product documentation (https://docs.ohc.network/).
• Ensure that UI text is placed in I18n files.
• Prepare a screenshot or demo video for the changelog entry and attach it to the issue.
• Request peer reviews.
• Complete QA on mobile devices.
• Complete QA on desktop devices.
• Add or update Playwright tests for related changes

[rbalogic]

Hi @rithviknishad 👋 Just bumping this whenever you get a chance to take a look. No rush, but let me know if you need any changes or if there's anything I can clarify! Thanks.