feat(test): add developer test-quick command

Add scripts/test-quick.sh and Makefile with:
- test-quick: runs ruff check + unit tests + smoke tests
- No real provider keys or platform accounts required
- Suitable for local branch self-test

Update tests/README.md:
- Document test-quick command
- Document test factories package
- Add smoke tests and factories directory structure

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

Makefile

@@ -0,0 +1,22 @@
+# LangBot Makefile
+# Quick developer commands
+
+.PHONY: test test-quick lint
+
+# Run all tests (full suite with coverage)
+test:
+	bash run_tests.sh
+
+# Quick self-test for developers (lint + unit + smoke, no real credentials needed)
+test-quick:
+	bash scripts/test-quick.sh
+
+# Run linting only
+lint:
+	ruff check src/langbot/ tests/
+	ruff format --check src/langbot/ tests/
+
+# Fix linting issues
+lint-fix:
+	ruff check --fix src/langbot/ tests/
+	ruff format src/langbot/ tests/