enhance(#4570): allow disabling planner stall detection (#4585)

* enhance(#4570): allow disabling planner stall detection

* docs(#4570): add changelog fragment

Emitted-Drift-Ack-Growth: plan-phase.md — the explicit opt-out gate covers all five planner and checker spawn classes
Emitted-Drift-Ack-Growth: settings-advanced.md — the toggle prompt and bounded-recovery warning expose the new setting

* chore(#4570): refresh compact-content baseline

* fix(#4570): preserve default-on watchdog fallback

* docs(#4570): qualify the chunked-mode orchestrator rules with the toggle

The two chunked-planning-mode stall-watch imperatives read as
unconditional, with the opt-out stated only in a following bullet. State
the PLANNER_STALL_DETECTION_ENABLED condition inline, matching the three
sites already qualified in plan-phase.md.

* chore(#4570): refresh compact-content baselines against rebased next

* fix(#4570): sync planner stall launcher

Keep the stall-detection helper aligned with the canonical runtime launcher.

* chore(#4570): refresh compact baseline after rebase

---------

Co-authored-by: Tom Boucher <trekkie@nomorestars.com>

tests/fixtures/compact-content-benchmark-baseline.json

@@ -28,9 +28,9 @@
       "reductionPct": 13.53
     },
     "plan-phase": {
-      "offTokens": 28000,
-      "onTokens": 24649,
-      "reductionPct": 11.97
+      "offTokens": 28406,
+      "onTokens": 25055,
+      "reductionPct": 11.8
     },
     "verify-work": {
       "offTokens": 13445,
@@ -39,8 +39,8 @@
     }
   },
   "aggregate": {
-    "offTokens": 108858,
-    "onTokens": 91988,
-    "reductionPct": 15.5
+    "offTokens": 109264,
+    "onTokens": 92394,
+    "reductionPct": 15.44
   }
 }