feat(mcp): add task discovery tools

[pablojaku]

Summary

• add list_tasks and get_task MCP tools with deterministic JSON responses
• extract user-scoped task query helpers shared by UI actions and MCP handlers
• add tasks:read and tasks:write to newly generated tokens without changing legacy token authority
• document task scopes and add routing/unit coverage

Part of #119.

Verification

• npm run lint
• npm test -- --run (239 files, 2,881 tests)
• npm run build
• MCP routing evals with local Qwen 3.5 9.7B (9/9)
• Chromium task E2E coverage passed on isolated port 3738

E2E baseline note

The full Chromium run passed 87/92 in parallel. Four unrelated job tests passed when rerun serially after aligning the fresh local database with their Draft/Applied ordering assumption. One unrelated profile deletion assertion remained stale in the UI even though SQLite confirmed the resume row was deleted.