docs(02-04): complete diagram hash linking gap closure plan

- SUMMARY.md documenting diagram hash linking and test stability fixes
- STATE.md updated with position, decisions, metrics
- ROADMAP.md updated with phase 02 plan progress
- REQUIREMENTS.md DIAG-02 marked complete

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

.planning/config.json

@@ -8,6 +8,7 @@
     "research": true,
     "plan_check": true,
     "verifier": true,
-    "nyquist_validation": true
+    "nyquist_validation": true,
+    "_auto_chain_active": false
   }
-}
+}