feat(test): add developer quality gate consolidation (G-007)

- Add scripts/test-integration-fast.sh for fast integration tests
- Add scripts/test-coverage.sh with 12% baseline threshold
- Update Makefile with test-integration-fast, test-coverage, test-all-local
- Update CI workflow with integration and coverage jobs
- Add smoke marker to pytest.ini
- Update tests/README.md with quality gate layers documentation
- Add tests/integration/pipeline/ for pipeline stage-chain tests

Quality gate layers:
- Quick: ruff + unit + smoke (~2 min)
- Fast Integration: SQLite/API/Pipeline (~3 min)
- Coverage: 12% threshold gate (~8 min)
- Full Local: all three combined

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Makefile

@@ -1,7 +1,7 @@
 # LangBot Makefile
 # Quick developer commands
 
-.PHONY: test test-quick lint
+.PHONY: test test-quick test-integration-fast test-coverage test-all-local lint
 
 # Run all tests (full suite with coverage)
 test:
@@ -11,6 +11,20 @@ test:
 test-quick:
 	bash scripts/test-quick.sh
 
+# Fast integration tests (SQLite/API/Pipeline, no external services)
+test-integration-fast:
+	bash scripts/test-integration-fast.sh
+
+# Coverage gate (all tests, enforces minimum threshold)
+test-coverage:
+	bash scripts/test-coverage.sh
+
+# Full local quality gate (quick + integration + coverage)
+test-all-local:
+	bash scripts/test-quick.sh
+	bash scripts/test-integration-fast.sh
+	bash scripts/test-coverage.sh
+
 # Run linting only
 lint:
 	ruff check src/langbot/ tests/