docs: add Kairn memory MCP + resource evaluations + guide updates

- guide/ultimate-guide.md §10.2: Add Kairn (knowledge graph memory with biological decay)
  - Typed relationships (depends-on, resolves, causes), 18 MCP tools
  - Updated comparison table: Serena / grepai / doobidoo / Kairn
  - Added decision routing for long-term memory + causality tracking
- guide/ultimate-guide.md §5.1: Add real-world CLAUDE.md migration example (Avo, 600-line → 15 path-scoped files)
- guide/ai-ecosystem.md: Minor update
- machine-readable/reference.yaml: Add Kairn entries
- examples/config/mcp.json: Add Kairn MCP config
- docs/resource-evaluations/: Add 2 new evaluations (context-evaluator-packmind, kairn-memory-mcp)
- docs/resource-evaluations/agents-md-empirical-study: Add community reception section
- docs/resource-evaluations/2026-02-23-agentsview: Minor fix

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/config/mcp.json

@@ -38,6 +38,11 @@
       "command": "memory",
       "args": ["server"],
       "description": "Semantic memory with cross-session search (complements Serena)"
+    },
+    "kairn": {
+      "command": "python",
+      "args": ["-m", "kairn", "serve"],
+      "description": "Knowledge graph memory with biological decay — auto-expires stale info (complements doobidoo/Serena)"
     }
   }
 }