refactor: Remove hooks - SessionEnd/PreCompact not useful for notifications

Hooks execute after Claude Code exits, so output is not visible.
Removed: setup command, install-hooks.sh, hooks.json, session-end-reminder.sh
Bump version to 2.2.0

🤖 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": "2.1.4",
+      "version": "2.2.0",
       "keywords": ["learn", "memory", "patterns", "gotchas", "domains", "cleanup", "hygiene"]
     }
   ]