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).

CLAUDE.md

@@ -131,8 +131,10 @@ was user-accepted 2026-07-29. **Campaign P — physics retail-feel parity
 (`docs/plans/2026-07-29-physics-parity-campaign.md`) is the ACTIVE
 user-directed detour** closing every physics-scope gap from the 2026-07-29
 audit (stat-coupled movement, response-layer edge family, remote residuals,
-entry restrictions/water, #262/#153/#167, ledger). Vendor browsing (Slice 5)
-and authoritative vendor transactions resume after Campaign P closes.
+entry restrictions/water, #262/#153/#167, ledger). P5 item 1 (#167,
+ConstraintManager leash constants + arming) is CLOSED 2026-07-30; #153 and
+#72 remain open in P5. Vendor browsing (Slice 5) and authoritative vendor
+transactions resume after Campaign P closes.
 
 **Modern Runtime/performance status:** Slices A–K of
 `docs/plans/2026-07-24-modern-runtime-architecture.md` are complete. Slice L is