feat: complete MCP traffic isolation — add missing endpoints, remove leaky path routing

[sap-yuan]

Summary

Phase 2 of DIARCHERS-1396: fully isolate MCP token traffic to /api/v1/mcp/*.

The original implementation used a client-side mcpPath() regex translation layer that only covered 6 paths. Any tool method not in that mapping would silently fall through to /api/v1/* regular traffic, defeating the isolation goal.

Backend — 6 new MCP endpoints

All new endpoints carry the full middleware stack: mcp_auth_required → @mcp_rate_limit → check_project_access_mcp → handler → audit_mcp.

Endpoint	File
GET /api/v1/mcp/projects/<id>	projects.py
GET /api/v1/mcp/projects/<id>/builds/<bid>	builds.py
GET /api/v1/mcp/projects/<id>/jobs/<jid>	jobs.py
GET /api/v1/mcp/projects/<id>/jobs/<jid>/stats	jobs.py
GET /api/v1/mcp/projects/<id>/jobs/<jid>/testruns	jobs.py
GET /api/v1/mcp/projects/<id>/jobs/<jid>/manifest	jobs.py

Also extracted _ACCESS_DENIED and _JOB_BY_PROJECT constants in jobs.py to eliminate string duplication.

Test plan

• All 6 new endpoints return data with a valid ib_mcp_* token
• All 6 new endpoints return 403 for a token without project scope
• Existing endpoints (list_projects, list_builds, list_jobs, get_job_log, list_job_artifacts, trigger) still work
• mcp_access_log contains entries for all new endpoint calls

[liuwei08]

Two must-fix issues found. See inline comments for details.

[sap-yuan]

Fixed both review findings in 15038b1:

[Blocker] Duplicate class definitions in builds.py — Confirmed valid. The old MCPBuilds, MCPTrigger, and _build_dict definitions (lines 170–275) were left over from the original file and not removed when the new code was added at the top. Deleted all duplicate definitions. Each class is now defined exactly once.

[High] Silent stats parse failure in jobs.py — Confirmed valid. Added import logging + logger = logging.getLogger('mcp_jobs'), replaced except Exception: pass with a warning log + audit_mcp(..., outcome='partial', error=...) so parse failures are observable in both application logs and the audit trail.

[liuwei08]

LGTM