feat(graceful-handoff): initial plugin with /graceful-handoff command

New plugin that produces a complete session handoff in under 60s:
NEXT-SESSION artifact, commit+push, and copy-paste prompt for next
session. Built for context-constrained models like Opus 4.7 where
sessions fill fast.

- Single declarative command, no hooks/agents/skills
- Detects handoff type: multi-session / plugin-work / single-task
- Default filename NEXT-SESSION-PROMPT.local.md; slug-override
- Flags: --no-commit, --dry-run
- Auto-generated Conventional Commits message from git diff --stat
- Respects pre-commit hooks (secrets, pathguard) — never bypasses

Also: add *.local.md to root .gitignore (existing NEXT-SESSION files
were untracked but not ignored) and list plugin in marketplace
README + CLAUDE.md per docs-convention.

CLAUDE.md

@@ -8,6 +8,7 @@ Open-source Claude Code plugin marketplace. Solo project by Kjell Tore Guttormse
 plugins/
   ai-psychosis/          v1.0.0  — Interaction awareness (sycophancy, reinforcement loops)
   config-audit/          v3.1.0  — Configuration intelligence (health, opportunities, auto-fix, whats-active)
+  graceful-handoff/      v1.0.0  — Session handoff in <60s (NEXT-SESSION artifact + commit+push + copy-paste prompt)
   linkedin-thought-leadership/  v1.2.0  — LinkedIn content pipeline + analytics
   llm-security/          v6.0.0  — Security scanning, auditing, threat modeling
   ms-ai-architect/       v1.8.0  — Microsoft AI architecture (Cosmo Skyberg persona)