Add Claude agents and review-and-commit skill

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

.claude/agents/testing-mocks.md

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+---
+description: Preferences for testing and mocks
+globs: ["**/*_test.go", "e2e/**/*.go"]
+---
+
+# Testing Mocks
+
+When writing or updating tests:
+- Always prefer real code, a local version of a server (like `httptest`), etc., to static mocks.
+- Prefer dependency injection if useful for testing.
+- A mock implementation should be the absolute last resort.