Step 8: Polish — lint, clock abstraction, e2e test.

- golangci-lint config with errcheck, govet, staticcheck, errorlint
- Fix all lint issues (unchecked error returns in cleanup paths, De Morgan)
- Inject jonboulle/clockwork into Garden for deterministic timestamps
- Add manifest.NewWithTime() for clock-aware initialization
- E2e lifecycle test: init → add → checkpoint → modify → status → restore → verify
- Update CLAUDE.md, PROJECT_PLAN.md, PROGRESS.md

Phase 1 (local) is now complete. All 9 CLI commands implemented and tested.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

go.mod

@@ -4,6 +4,7 @@ go 1.25.7
 
 require (
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/jonboulle/clockwork v0.5.0 // indirect
 	github.com/spf13/cobra v1.10.2 // indirect
 	github.com/spf13/pflag v1.0.9 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect