feat(baseline): clear context and branch-first at spec boundaries

[protonspy]

Summary

Folds two spec-boundary workflow-discipline steps into the shipped baseline templates (internal/templater/templates/), so downstream csdd init/update users get them:

• /clear at each feature/spec boundary — start a spec on a clean context and reset once its PR ships. The Stop hook (test-before-stop.sh) nudges the operator when a spec's tasks.md is fully checked.
• Branch-first before implementation — git switch -c <type>/<feature> (kebab-case: feat/ fix/ chore/ refactor/ docs/ test/ perf/), enforced by the PreToolUse hook (block-destructive.sh), which now blocks git commit/git push on the default branch.

Touches the CLAUDE.md workflow, the SDD guide loop (§9.2), the wf-development agent, and the test-before-stop / block-destructive hooks. No spec — a direct workflow adjustment requested by the maintainer. (Layer-3 .claude//CLAUDE.md copies are gitignored; this PR carries the baseline .tmpl source, which csdd update dogfoods locally.)

Verification

go vet ./...            ✅
go test -race ./...     ✅  (pre-push gate; all packages green, ~85% cli coverage)
guard-hook behavior     ✅  blocks commit/push on main|master, allows on feature
                            branches, no false-positives, no crash on non-git dirs
gofmt -l .              ⚠️  only 3 pre-existing CRLF-churn files (unrelated, not in this PR)

🤖 Generated with Claude Code