feat(#313): Implement FastAPI and agent tracing instrumentation

Add comprehensive OpenTelemetry distributed tracing to the coordinator
FastAPI service with automatic request tracing and custom decorators.

Implementation:
- Created src/telemetry.py: OTEL SDK initialization with OTLP exporter
- Created src/tracing_decorators.py: @trace_agent_operation and
  @trace_tool_execution decorators with sync/async support
- Integrated FastAPI auto-instrumentation in src/main.py
- Added tracing to coordinator operations in src/coordinator.py
- Environment-based configuration (OTEL_ENABLED, endpoint, sampling)

Features:
- Automatic HTTP request/response tracing via FastAPIInstrumentor
- Custom span enrichment with agent context (issue_id, agent_type)
- Graceful degradation when telemetry disabled
- Proper exception recording and status management
- Resource attributes (service.name, service.version, deployment.env)
- Configurable sampling ratio (0.0-1.0, defaults to 1.0)

Testing:
- 25 comprehensive tests (17 telemetry, 8 decorators)
- Coverage: 90-91% (exceeds 85% requirement)
- All tests passing, no regressions

Quality:
- Zero linting errors (ruff)
- Zero type checking errors (mypy)
- Security review approved (no vulnerabilities)
- Follows OTEL semantic conventions
- Proper error handling and resource cleanup

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

apps/coordinator/pyproject.toml

@@ -11,6 +11,10 @@ dependencies = [
     "python-dotenv>=1.0.0",
     "anthropic>=0.39.0",
     "slowapi>=0.1.9",
+    "opentelemetry-api>=1.20.0",
+    "opentelemetry-sdk>=1.20.0",
+    "opentelemetry-instrumentation-fastapi>=0.41b0",
+    "opentelemetry-exporter-otlp>=1.20.0",
 ]
 
 [project.optional-dependencies]