fix(tasks): sync poll no longer remounts board; Issue comments in sheet

[ReBoticsAI]

Summary

• Background GitHub Project sync poll no longer bumps boardKey / remounts ProjectsBoard, so an open task Sheet stays open; cards soft-merge on syncRevision (last_synced_at) changes.
• Linked Issue/PR cards fetch and display GitHub Issue comments; posting comments uses the connected GitHub token (Issues R/W). Local-only cards keep GodMode card comments.
• Wider sheet with issue header link for a closer GitHub-issue feel.

Test plan

• Open /tasks on a linked board, open a card Sheet, wait for sync poll (~30s); sheet stays open and board does not flash
• Manual Sync GitHub updates cards without closing the Sheet
• Linked Issue card shows Issue comments with author/avatar; post a comment and see it appear
• Draft Project item shows draft notice (no Issue comments)
• Local-only board still uses GodMode activity comments
• npx vitest run apps/bridge/src/services/__tests__/github-projects-comments.test.ts

Closes #293

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