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/.claude-plugin/plugin.json

@@ -0,0 +1,19 @@
+{
+  "name": "graceful-handoff",
+  "version": "1.0.0",
+  "description": "Produce session-handoff artifacts, commit and push pending work, and print a copy-paste prompt for the next session. Designed for context-constrained models like Opus 4.7 where sessions fill fast.",
+  "author": {
+    "name": "Kjell Tore Guttormsen"
+  },
+  "auto_discover": true,
+  "license": "MIT",
+  "repository": "https://git.fromaitochitta.com/open/ktg-plugin-marketplace",
+  "keywords": [
+    "session",
+    "handoff",
+    "context-management",
+    "opus-4.7",
+    "git",
+    "workflow"
+  ]
+}