chore: add 17 operational rules and rule index

- Create .claude/rules/ with all 17 standard rule files (01-security through 17-document-imports)
- Add Operational Rules section with Rule Index to .claude/CLAUDE.md

.claude/rules/06-testing.md

@@ -0,0 +1,24 @@
+# Testing
+
+Assume nothing about correctness — prove it with tests.
+
+## Unit Tests
+
+- Write the test first for non-trivial logic (TDD). Implement until it passes.
+- Every new function/method/module with logic gets unit tests.
+- Run existing tests after every change. Fix breaks before moving on.
+
+## Integration Tests
+
+- Test module boundaries: DB queries, external APIs, filesystem, message queues.
+- Use real dependencies (or containers) — not mocks. Mocks belong in unit tests.
+- Target 70/20/10 ratio: unit/integration/E2E.
+
+## End-to-End Tests
+
+- Critical user journeys only (~10% of suite). Test API endpoints with integration tests, not E2E.
+
+## After Every Change
+
+- Run the test suite, report results, fix failures before continuing.
+- If no test framework exists, flag it and propose a testing strategy.