fix(physics): P5 commit 3 - retire TS-35, close #167 (ConstraintManager leash)

PhysicsBody.IsFullyConstrained now reflects real ConstraintManager state
(pushed every tick by the same per-tick pumps commit 2 wired), so
jump_is_allowed's already-ported gate (WeenieError 0x47) actually fires
while an object is rubber-banding hard against a server position
correction, closing the last piece of #167.

Housekeeping:
- Delete register row TS-35 (retired: the write side is no longer stubbed).
- Rewrite the stale doc comments on PhysicsBody.IsFullyConstrained,
  ConstraintManager (class + IsFullyConstrained), PositionManager.ConstrainTo,
  EntityPhysicsHost.PositionManager, and PlayerMovementController.PositionManager
  that described the leash as permanently unarmed/stubbed.
- Close #167 in ISSUES.md citing the research doc and commits e0629145 /
  7719d25b.
- Add an "as-ported" addendum to
  docs/research/2026-07-30-constraint-leash-constants.md naming the actual
  current seam owners (the doc's own open question flagged this as
  implementer-verify-required post-J-slices).
- Update docs/plans/2026-07-29-physics-parity-campaign.md's P5 status and
  CLAUDE.md's Campaign P summary to reflect #167's closure (items #153/#72
  remain open in P5).

Verification: complete solution suite green - 9,978 tests, 5 skips, 0
failures across all 9 test projects (Core.Tests, Runtime.Tests, App.Tests,
Headless.Tests, Core.Net.Tests, Content.Tests, UI.Abstractions.Tests,
Bake.Tests, Cli.Tests).

src/AcDream.Runtime/Gameplay/PlayerMovementController.cs

@@ -503,7 +503,11 @@ public sealed class PlayerMovementController
     /// motion) and <c>UseTime</c> after the completed-motions sweep (retail
     /// <c>UpdateObjectInternal</c> tail @0x005159b3 — the sticky 1 s lease
     /// watchdog). <see cref="SetPosition(Vector3, uint, Vector3)"/> tears any
-    /// stick down (retail <c>teleport_hook</c> @0x00514eee).
+    /// stick down (retail <c>teleport_hook</c> @0x00514eee) and, as of
+    /// Campaign P P5 (#167), also tears down and immediately re-arms the
+    /// constraint leash (<c>UnConstrain</c> then <c>ConstrainTo</c>);
+    /// <see cref="BlipPosition"/> arms the leash without tearing it down first
+    /// (retail <c>SmartBox::BlipPlayer</c> survives motion/velocity/stick).
     /// </summary>
     public AcDream.Core.Physics.Motion.PositionManager? PositionManager { get; set; }