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/Chat/ChatPanel.cs

@@ -42,6 +42,14 @@ public sealed class ChatPanel : IPanel
     // entries without yanking the user's manual scroll.
     private int _lastRenderedCount;
 
+    // Phase K.2: one-shot focus request for the chat input. Set by
+    // FocusInput() (driven by Tab → ToggleChatEntry); the next Render
+    // call emits SetKeyboardFocusHere immediately before the input
+    // field and clears the flag. Without the one-shot semantics, the
+    // panel would steal focus on every frame and the user could never
+    // click into another widget.
+    private bool _focusRequested;
+
     public ChatPanel(ChatVM vm)
     {
         _vm = vm ?? throw new ArgumentNullException(nameof(vm));
@@ -56,6 +64,15 @@ public sealed class ChatPanel : IPanel
     /// <inheritdoc />
     public bool IsVisible { get; set; } = true;
 
+    /// <summary>
+    /// Phase K.2: request keyboard focus for the chat input on the
+    /// NEXT <see cref="Render"/>. One-shot — fires once and resets,
+    /// so callers (e.g. <c>GameWindow</c>'s Tab handler subscribing to
+    /// <c>ToggleChatEntry</c>) can drive it on a single key press
+    /// without trapping the user permanently in the input field.
+    /// </summary>
+    public void FocusInput() => _focusRequested = true;
+
     /// <inheritdoc />
     public void Render(PanelContext ctx, IPanelRenderer renderer)
     {
@@ -115,6 +132,15 @@ public sealed class ChatPanel : IPanel
         // Phase I.4: input field. Backend implementation clears _input
         // on submit per the IPanelRenderer contract.
         renderer.Separator();
+        // Phase K.2: honor a pending FocusInput() request — emit
+        // SetKeyboardFocusHere immediately before the input widget so
+        // ImGui (or the future custom backend) applies it to that
+        // field. One-shot: clear the flag after firing.
+        if (_focusRequested)
+        {
+            renderer.SetKeyboardFocusHere();
+            _focusRequested = false;
+        }
         if (renderer.InputTextSubmit("##chatinput", ref _input, InputBufferMaxLen, out var submitted)
             && submitted is not null)
         {