feat: bake iac_source_catalog into Docker image; fix YAML smoke test; add .gitignore

- Dockerfile: COPY iac_source_catalog.json in builder + final stage
- push_catalogs.sh: cp iac_source_catalog.json to iLSP repo root before SCP
- smoke_test_completions.py: detect WS CLOSE in _recv_until_id; 20s YAML init timeout; clearer error message
- .gitignore: standard Python exclusions

Fixes: iac_source_modules=0 (was never baked into image)

.gitignore

@@ -0,0 +1,14 @@
+__pycache__/
+*.pyc
+*.pyo
+.pytest_cache/
+.eggs/
+*.egg-info/
+dist/
+build/
+.coverage
+htmlcov/
+*.log
+.env
+.venv/
+venv/