feat: Add /learn:setup command for hook installation

- Add setup.md command to install SessionEnd and PreCompact hooks
- Add install-hooks.sh script for automatic hook installation to ~/.claude/settings.json
- Hooks remind user to run /learn:analyze before session end or auto-compact
- Bump version to 2.1.2

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -11,7 +11,7 @@
       "name": "learn",
       "source": "./plugins/learn",
       "description": "Domain-based memory with selective saving, signal detection, and memory hygiene",
-      "version": "2.1.1",
+      "version": "2.1.2",
       "keywords": ["learn", "memory", "patterns", "gotchas", "domains", "cleanup", "hygiene"]
     }
   ]