feat(#370): install mosaicstack-telemetry in Coordinator

- Add mosaicstack-telemetry>=0.1.0 to pyproject.toml dependencies
- Configure Gitea PyPI registry via pip.conf (extra-index-url)
- Integrate TelemetryClient in FastAPI lifespan (start_async/stop_async)
- Store client on app.state.mosaic_telemetry for downstream access
- Create mosaic_telemetry.py helper module with:
  - get_telemetry_client(): retrieve client from app state
  - build_task_event(): construct TaskCompletionEvent with coordinator defaults
  - create_telemetry_config(): create config from MOSAIC_TELEMETRY_* env vars
- Add 28 unit tests covering config, helpers, disabled mode, and lifespan
- New module has 100% test coverage

Refs #370

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/coordinator/pyproject.toml

@@ -15,6 +15,7 @@ dependencies = [
     "opentelemetry-sdk>=1.20.0",
     "opentelemetry-instrumentation-fastapi>=0.41b0",
     "opentelemetry-exporter-otlp>=1.20.0",
+    "mosaicstack-telemetry>=0.1.0",
 ]
 
 [project.optional-dependencies]