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.

plugins/graceful-handoff/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Kjell Tore Guttormsen
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.