✨ Add project and file discovery to penpotMgmt

Discovery:
- Add listProjects and project-scoped listFiles with content:read checks.
- Return metadata from existing RPCs in dashboard and workspace contexts.
- Reject invalid IDs and preserve backend access errors.

Documentation:
- Keep usage in API type comments and include regenerated MCP API docs.
- Remove README implementation details and consolidate the changelog.
- Add usage information to the MCP server's initial instructions

Validation:
- Pass 8 frontend tests, 81 runtime tests and the runtime build.
- Verify both APIs through live MCP calls in dashboard and workspace.
- Pass type, lint, formatting and diff checks.

AI-assisted-by: gpt-6
Signed-off-by: Dominik Jain <dominik.jain@oraios-ai.de>
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