chore(orchestrator): Phase 5 complete - all 17 tasks done + verification

Issue #340: Low Priority - Cleanup + Performance
- 26 findings across 7 CQ + 19 SEC-Low, all remediated
- 2 findings pre-completed from Phase 4 (CQ-API-7, CQ-ORCH-9)
- Test counts: api=2432, web=786, orchestrator=682

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

docs/orchestrator-learnings.json

@@ -193,6 +193,27 @@
         "ui": 11
       },
       "completed_at": "2026-02-06T14:22:00Z"
+    },
+    {
+      "phase": 5,
+      "name": "Low Priority - Cleanup + Performance",
+      "issue": "#340",
+      "total_tasks": 17,
+      "completed": 17,
+      "failed": 0,
+      "deferred": 0,
+      "total_estimate_k": 155,
+      "total_actual_k": 878,
+      "variance_pct": 466,
+      "analysis": "Phase 5 estimates were consistently 5-6x lower than actual usage. Primary drivers: (1) workers spend significant tokens reading context files before implementing fixes, (2) comprehensive test creation dominates usage, (3) multi-finding batched tasks (e.g. MS-P5-009 at 93K for 2 findings) expand beyond estimates. All 17 tasks completed successfully with zero failures across 26 findings.",
+      "test_counts": {
+        "api": 2432,
+        "web": 786,
+        "orchestrator": 682,
+        "shared": 17,
+        "ui": 11
+      },
+      "completed_at": "2026-02-06T18:54:00Z"
     }
   ],
   "proposed_adjustments": [