feat(input): #24 Phase K.2 - auto-enter player mode at login + MMB mouse-look + DebugPanel free-fly + Tab to chat-input focus

Five changes:

1. PlayerModeAutoEntry — testable guard class that fires once after
   EnterWorld + WorldSession.State.InWorld + player entity present +
   PlayerController.State == InWorld. GameWindow arms the entry
   after EnterWorld; per-frame Tick checks all four guards and
   invokes the same fly-to-player transition the Tab handler runs.
   User-initiated fly toggle (DebugPanel button) Cancel()s pending
   entry. Skip in offline mode (no ACDREAM_LIVE) — Holtburg orbit
   stays default for testing.

2. MouseLookState + KeyBindings.RetailDefaults() binds MMB Hold to
   InputAction.CameraInstantMouseLook. GameWindow subscribes:
   - Press: hide cursor, capture position, _mouseLookActive = true.
   - Release: restore cursor, deactivate.
   - WantCaptureMouse=true while held → suspend (release cursor).
   - MouseMove while active: combined drive — chase camera yaw +
     character heading move together (retail's signature mouse-look
     behavior). Camera Y still pitches camera-only.

3. DebugPanel "Toggle Free-Fly Mode" button via DebugVM.ToggleFlyMode
   action delegate — replaces the F-key as the primary discovery
   path for free-fly. Gated on DevToolsEnabled.

4. ChatPanel.FocusInput() one-shot + IPanelRenderer.SetKeyboardFocusHere
   primitive. GameWindow's ToggleChatEntry (Tab) subscriber calls
   _chatPanel.FocusInput() so Tab moves focus to the chat input
   field. Replaces the K.1c TODO stub.

5. WantCaptureMouse gating reinforcement on surviving mouse handlers
   (no new code; verified intact from K.1b).

21 new tests (8 PlayerModeAutoEntry, 10 MouseLookState, 3 ChatPanel
focus). 1183 total green. 0 warnings, 0 errors.

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

src/AcDream.UI.Abstractions/Panels/Debug/DebugPanel.cs

@@ -211,6 +211,12 @@ public sealed class DebugPanel : IPanel
         r.SameLine();
         if (r.Button("Toggle collision wires")) _vm.ToggleCollisionWires?.Invoke();
 
+        // Phase K.2 — explicit free-fly toggle button. Mirrors the
+        // legacy F-key alias but is discoverable to users who haven't
+        // memorized the Ctrl+F* debug bindings. Action handle owned
+        // by GameWindow; null-safe for tests / offline.
+        if (r.Button("Toggle Free-Fly Mode")) _vm.ToggleFlyMode?.Invoke();
+
         r.Text(_vm.DebugWireframes ? "collision wires: ON" : "collision wires: OFF");
     }