feat(tdd-from-schema): generate response schema snapshot tests

[PAMulligan]

Summary

• Adds snapshot test generation to the tdd-from-schema skill so every generated suite captures response body keys, full normalized bodies, headers, and error envelopes — catching added/removed/renamed fields that status-code assertions miss.
• Introduces normalizeForSnapshot / responseShape / snapshotHeaders helpers that strip UUIDs and ISO timestamps so snapshots stay stable across runs without losing schema-drift detection.
• Uses toMatchInlineSnapshot() for contract-critical bits (top-level keys, error codes, headers) so breakage shows up in the test file at code-review time, and toMatchSnapshot() for full normalized bodies stored under tests/routes/__snapshots__/.
• Documents the vitest -u workflow for intentional contract changes and updates the skill's Output table to list the new artifacts.

Closes #47

Test plan

• Run /build-from-schema end-to-end against a sample OpenAPI spec and confirm *.snapshot.test.ts files are emitted per resource
• Verify generated snapshot tests fail in RED (no handlers) alongside the rest of the suite
• Confirm snapshots are created on first GREEN run and subsequent runs pass
• Intentionally change a response shape and confirm pnpm vitest run -u regenerates snapshots cleanly
• CI passes on this branch

🤖 Generated with Claude Code