chore: Simplify hook messages - remove decorations and emojis

- Plain text messages for SessionEnd and PreCompact hooks
- Use echo instead of printf
- Bump version to 2.1.4

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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": "2.1.3",
+      "version": "2.1.4",
       "keywords": ["learn", "memory", "patterns", "gotchas", "domains", "cleanup", "hygiene"]
     }
   ]