feat(session-handoff): add PostToolUse commit-detector hook [v0.3.0]

Hooks live in skills/session-handoff/hooks/:
- commit-detector.ps1  Windows/PowerShell
- commit-detector.sh   POSIX (python3 for JSON parsing)
- README.md            opt-in instructions, cross-platform settings.json
                       snippets, smoke procedure

Hook reads PostToolUse stdin, detects substantive `git commit` (prefix
not in meta/docs/style/chore + fix typo, AND body >200 chars OR files >3).
On hit, emits hookSpecificOutput.additionalContext so Claude Code
surfaces a system reminder next iteration. Silent skip on --amend, failed
commits, non-git cwd, trivial prefix, below thresholds.

install.sh deliberately does NOT mutate settings.json — opt-in via the
README hook config snippet, applied once per machine. SKILL.md body
mentions the hook as an optional alternative to the agent-side
behavioral heuristic.

Bump 0.2.1 -> 0.3.0 MINOR (new opt-in capability, backward-compatible —
SKILL keeps working without the hook).

Deferred (separate follow-ups if needed):
- live-hook e2e smoke (would interfere with current session commits)
- rebase/cherry-pick batch deduplication

Closes [session-handoff-posttooluse-hook] (partial: stdin smoke,
live-hook deferred).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.tasks/STATUS.md

@@ -1,5 +1,5 @@
 # Task Board
-_Updated: 2026-05-24 (session-handoff: install + bootstrap-template-extend + hermes-mapping 🟢; 3 из 7 кластера закрыто.)_
+_Updated: 2026-05-24 (session-handoff: 3 baseline 🟢, posttooluse-hook + existing-projects-upgrade → 🔴.)_
 
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