fix(#121): Remediate security issues from ORCH-121 review

Priority Fixes (Required Before Production):

H3: Add rate limiting to webhook endpoint
- Added slowapi library for FastAPI rate limiting
- Implemented per-IP rate limiting (100 req/min) on webhook endpoint
- Added global rate limiting support via slowapi

M4: Add subprocess timeouts to all gates
- Added timeout=300 (5 minutes) to all subprocess.run() calls in gates
- Implemented proper TimeoutExpired exception handling
- Removed dead CalledProcessError handlers (check=False makes them unreachable)

M2: Add input validation on QualityCheckRequest
- Validate files array size (max 1000 files)
- Validate file paths (no path traversal, no null bytes, no absolute paths)
- Validate diff summary size (max 10KB)
- Validate taskId and agentId format (non-empty)

Additional Fixes:

H1: Fix coverage.json path resolution
- Use absolute paths resolved from project root
- Validate path is within project boundaries (prevent path traversal)

Code Review Cleanup:
- Moved imports to module level in quality_orchestrator.py
- Refactored mock detection logic into separate helper methods
- Removed dead subprocess.CalledProcessError exception handlers from all gates

Testing:
- Added comprehensive tests for all security fixes
- All 339 coordinator tests pass
- All 447 orchestrator tests pass
- Followed TDD principles (RED-GREEN-REFACTOR)

Security Impact:
- Prevents webhook DoS attacks via rate limiting
- Prevents hung processes via subprocess timeouts
- Prevents path traversal attacks via input validation
- Prevents malformed input attacks via comprehensive validation

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/coordinator/pyproject.toml

@@ -10,6 +10,7 @@ dependencies = [
     "pydantic-settings>=2.1.0",
     "python-dotenv>=1.0.0",
     "anthropic>=0.39.0",
+    "slowapi>=0.1.9",
 ]
 
 [project.optional-dependencies]