feat(learn): Explicit frontmatter + compact output messages

- Add explicit header example with HTML paths comment (Pas 6.1)
- Add v2.x → v3.0 migration instructions
- Compact all output messages (ultra-compact format)
- Remove EXCLUSE section from output
- Bump version to 3.2.0

🤖 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": "Minimalist memory format with domain-based storage and signal detection",
-      "version": "3.0.0",
+      "version": "3.2.0",
       "keywords": ["learn", "memory", "patterns", "gotchas", "domains", "minimalist"]
     }
   ]