fix(retail): rotation rate, useability gate, retail toast strings

Two retail divergences fixed from the 2026-05-16 faithfulness audit
(Commit A of the plan at docs/superpowers/plans/2026-05-16-retail-faithfulness-fixes.md).

1. Rotation rate ignored HoldKey.Run. Retail's CMotionInterp::
   apply_run_to_command (decomp 0x00527be0 line 305098) multiplies
   turn_speed by run_turn_factor (1.5, PDB-named symbol at 0x007c8914)
   when input is TurnRight/TurnLeft under HoldKey.Run. Effective
   running rotation is 50% faster (~135°/s vs walking ~90°/s).
   Our keyboard A/D and ApplyAutoWalkOverlay used a fixed walking
   rate.

   New: RemoteMoveToDriver.TurnRateFor(running) helper. Keyboard
   path passes input.Run; auto-walk overlay passes
   _autoWalkInitiallyRunning. The walking-rate base
   (BaseTurnRateRadPerSec = π/2) is unchanged; TurnRateRadPerSec
   constant is preserved as the walking-rate alias for callers
   that don't have run/walk state (NPC remotes).

2. IsUseableTarget gated on `useability & USEABLE_REMOTE (0x20)`,
   which was stricter than retail. Per ItemUses::IsUseable
   (acclient_2013_pseudo_c.txt:256455) cross-referenced with 4
   call sites, retail's IsUseable() semantic is `_useability != 0`.
   But visually retail's USEABLE_NO (1) entities don't approach
   either, because ACE never broadcasts MovementType=6 for them.
   Our client installs a speculative auto-walk BEFORE the server
   responds, so we'd visibly approach + face signs before the
   wire packet was rejected.

   Pragmatic fix: block USEABLE_UNDEF (0) AND USEABLE_NO (1) in
   IsUseableTarget — slightly stricter than retail's
   IsUseable but matches retail's user-visible behaviour
   ("R on sign does nothing"). Documented in the doc-comment so
   a future implementer knows the gap.

3. New IsPickupableTarget gate for F-key path — requires
   USEABLE_REMOTE (0x20) bit. Null-useability fallback for
   BF_CORPSE + small-item ItemTypes (preserves M1 ground-item
   pickup flow when ACE seed DB doesn't publish useability).

4. R-key (UseCurrentSelection) upfront gate now ALWAYS uses
   IsUseableTarget. R is conceptually "use" with smart-routing
   to pickup as a downstream optimization. F-key (SendPickUp)
   uses IsPickupableTarget directly.

5. Retail toast strings on block, centralised in new
   src/AcDream.Core/Ui/RetailMessages.cs:
   - "The X cannot be used" (data 0x007e2a70, sprintf 0x00588ea4)
     fires on UseCurrentSelection / SendUse gate block.
   - "The X can't be picked up!" (sprintf 0x00587353) fires on
     SendPickUp non-pickupable block.
   - "You cannot pick up creatures!" (data 0x007e22b4) fires on
     SendPickUp creature block (was previously silent).
   - Plus 4 inactive retail strings ready for future call sites:
     CannotBeUsedWith (two-target Use), CannotBePickedUp (formal
     pickup variant), CannotBeUsedWhileOnHook_HooksOff +
     CannotBeUsedWhileOnHook_NotOwner (housing). All cite their
     retail data addresses + runtime sprintf addresses.

6. ProbeUseabilityFallbackEnabled diagnostic (env var
   ACDREAM_PROBE_USEABILITY_FALLBACK=1) logs every time the
   null-useability fallback fires. Settles whether the
   fallback for creature + BF_DOOR/LIFESTONE/PORTAL/CORPSE
   entries in ACE's seed DB without useability is hot code
   or theoretical defense.

Test coverage:
- +3 RemoteMoveToDriverTests cover TurnRateFor walking/running/back-compat.
- +7 RetailMessagesTests cover each retail string with retail anchor.
- +1 CreateObjectTests TryParse_WeenieFlagsUsable_ReadsUseableNoValue
  pins parser correctness for USEABLE_NO=1.
- 294/294 Core.Net pass; 24/24 new+touched Core tests pass.
- Pre-existing baseline of 8 Physics test failures unchanged
  (BSPStepUp + MotionInterpreter regression noise from prior
  sessions; out of scope here).

Deferred to a separate session per user direction:
- Click area = indicator-rect retail fidelity. Retail's picker
  uses per-part CGfxObj.drawing_sphere + polygon refine
  (0x0054c740); ours uses single Setup.SelectionSphere ray-
  intersect. The rect corners are dead zones today. Three fix
  options analyzed: screen-space rectangle hit-test, sqrt(2)
  sphere inflation, polygon refine Stage B.

Plan: docs/superpowers/plans/2026-05-16-retail-faithfulness-fixes.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Input/PlayerMovementController.cs

@@ -502,7 +502,12 @@ public sealed class PlayerMovementController
             // MathF.Min(|delta|, maxStep) naturally clamps the final
             // fractional step to exactly delta, so we land on the
             // target heading without overshoot.
-            float maxStep = RemoteMoveToDriver.TurnRateRadPerSec * dt;
+            // 2026-05-16 — retail-faithful turn rate. Auto-walk knows
+            // its run/walk decision from _autoWalkInitiallyRunning
+            // (set at BeginServerAutoWalk based on initial distance vs
+            // WalkRunThreshold). Running rotation is 50% faster per
+            // run_turn_factor at retail 0x007c8914.
+            float maxStep = RemoteMoveToDriver.TurnRateFor(_autoWalkInitiallyRunning) * dt;
             Yaw += MathF.Sign(delta) * MathF.Min(MathF.Abs(delta), maxStep);
             while (Yaw >  MathF.PI) Yaw -= 2f * MathF.PI;
             while (Yaw < -MathF.PI) Yaw += 2f * MathF.PI;
@@ -637,10 +642,21 @@ public sealed class PlayerMovementController
         }
 
         // ── 1. Apply turning from keyboard + mouse ────────────────────────────
+        // 2026-05-16 — retail-faithful turn rate.
+        // Anchor: docs/research/named-retail/acclient_2013_pseudo_c.txt
+        //   - CMotionInterp::apply_run_to_command 0x00527be0
+        //     multiplies turn_speed by run_turn_factor (1.5) under
+        //     HoldKey.Run on TurnRight/TurnLeft commands.
+        //   - Base rate ±π/2 rad/s comes from add_motion 0x005224b0
+        //     with HasOmega-cleared MotionData fallback.
+        // Effective: walking ≈ 90°/s, running ≈ 135°/s.
+        // Previously: WalkAnimSpeed*0.5 ≈ 89.4°/s — coincidentally
+        // close to retail walking but no run differentiation.
+        float keyboardTurnRate = RemoteMoveToDriver.TurnRateFor(input.Run);
         if (input.TurnRight)
-            Yaw -= MotionInterpreter.WalkAnimSpeed * 0.5f * dt;  // ~90°/s
+            Yaw -= keyboardTurnRate * dt;
         if (input.TurnLeft)
-            Yaw += MotionInterpreter.WalkAnimSpeed * 0.5f * dt;
+            Yaw += keyboardTurnRate * dt;
         Yaw -= input.MouseDeltaX * MouseTurnSensitivity;
         // Wrap yaw to [-PI, PI] so it doesn't grow unbounded.
         while (Yaw > MathF.PI)  Yaw -= 2f * MathF.PI;