Sync hardened .claude governance tooling from reference repo #178

Bring the missing/hardened Claude governance surfaces (pr-author skill + receipt-enforced hook, missing referenced skills, hardened orchestrator/feature-review, schema, ci-workflows rule, validator wiring, generic agent-memories) into this repo, adapted to keep the current policy (80/90 coverage, MSTest/Moq, csharpier+msbuild+vstest, PoshQC+Pester, COM/VSTO). Excludes the reference repo's 85/75 coverage, 7-stage toolchain, quality-tiers, architecture-boundary/benchmark gates, and Python/TypeScript-specific docs. C# analyzer-stack hardening deferred to a separate validated PR.