feat(ui): debug overlay + refined input controls

Adds the first on-screen HUD for the dev client plus today's mouse-control
refinements. Also lands yesterday's scenery-alignment changes that were
left uncommitted in the working tree.

Overlay:
- BitmapFont rasterizes a system TTF via StbTrueTypeSharp into a 512x512
  R8 atlas at startup (Consolas on Windows, DejaVu/Menlo fallbacks)
- TextRenderer batches 2D quads in screen-space with ortho projection;
  one shader + two draw calls (rect then text) for panel backgrounds
  under glyphs
- DebugOverlay composes info / stats / compass / help panels on top of
  the 3D scene; toggles via F1/F4/F5/F6; transient toasts for key events
- DebugLineRenderer and its shaders (carried over from the scenery work)
  are properly committed in this commit

Controls:
- Per-mode mouse sensitivity (Chase 0.15, Fly 1.0, Orbit 1.0); F8/F9 to
  adjust the active mode multiplicatively (x1.2)
- Hold RMB to free-orbit the chase camera around the player; release
  stays at the new angle (no snap-back)
- Mouse-wheel zooms chase distance between 2m and 40m
- Chase pitch widened to [-0.7, 1.4] so mouse-Y tilts both ways from
  the default neutral angle

Scenery alignment (carried from yesterday's session):
- ShadowObjectRegistry AllEntriesForDebug + Scale field
- SceneryGenerator uses ACViewer's OnRoad polygon test + baseLoc +
  set_heading rotation
- BSPQuery dispatchers accept localToWorld so normals/offsets transform
  correctly per part
- TransitionTypes.CylinderCollision rewritten with wall-slide + push-out
- PhysicsDataCache caches visual-mesh AABB for scenery that lacks
  physics Setup bounds

src/AcDream.App/Rendering/ChaseCamera.cs

@@ -14,17 +14,34 @@ public sealed class ChaseCamera : ICamera
     public float Aspect { get; set; } = 16f / 9f;
     public float FovY { get; set; } = MathF.PI / 3f;
 
-    /// <summary>Distance behind the player.</summary>
+    /// <summary>Distance behind the player. Clamped to [<see cref="DistanceMin"/>, <see cref="DistanceMax"/>].</summary>
     public float Distance { get; set; } = 8f;
+    public const float DistanceMin = 2f;
+    public const float DistanceMax = 40f;
 
     /// <summary>Camera pitch above horizontal (radians). Positive = look down.</summary>
     public float Pitch { get; set; } = 0.35f;  // ~20 degrees
 
+    /// <summary>
+    /// Additional yaw applied on top of the player's heading when positioning
+    /// the camera. Used by the hold-RMB "inspect" mode to orbit around the
+    /// player without rotating the character. Snap to 0 to return the camera
+    /// to directly behind the player.
+    /// </summary>
+    public float YawOffset { get; set; } = 0f;
+
     /// <summary>Vertical offset from the player's feet to the look-at point (eye height).</summary>
     public float EyeHeight { get; set; } = 1.5f;
 
-    private const float PitchMin = 0.05f;
-    private const float PitchMax = 1.4f;  // ~80 degrees
+    // Pitch range: negative values place the camera below the player's Z
+    // (at distance * sin(Pitch)) so the player can be viewed from a low
+    // angle. Clamped to -0.7 to avoid pushing the camera deep underground;
+    // at -0.7 and Distance=8 the camera is ~5m below player-Z which will
+    // clip terrain on hills but is OK on flat ground. 1.4 ≈ looking
+    // straight down. Wider than the old [0.05, 1.4] so mouse-Y moves the
+    // camera in both directions from the neutral [~20°] default.
+    private const float PitchMin = -0.7f;
+    private const float PitchMax = 1.4f;
 
     private float _playerYaw;
     private Vector3 _lookAt;
@@ -43,9 +60,11 @@ public sealed class ChaseCamera : ICamera
         _playerYaw = playerYaw;
         _lookAt = playerPosition + new Vector3(0f, 0f, EyeHeight);
 
-        // Camera offset: behind the player (-forward direction) and above.
-        float forwardX = MathF.Cos(playerYaw);
-        float forwardY = MathF.Sin(playerYaw);
+        // Camera offset: behind the player (-forward direction) plus any
+        // YawOffset for the hold-RMB inspect orbit mode.
+        float effectiveYaw = playerYaw + YawOffset;
+        float forwardX = MathF.Cos(effectiveYaw);
+        float forwardY = MathF.Sin(effectiveYaw);
 
         float horizontalDist = Distance * MathF.Cos(Pitch);
         float verticalDist = Distance * MathF.Sin(Pitch);
@@ -63,4 +82,12 @@ public sealed class ChaseCamera : ICamera
     {
         Pitch = Math.Clamp(Pitch + delta, PitchMin, PitchMax);
     }
+
+    /// <summary>
+    /// Adjust distance (zoom) by a delta, clamped to [DistanceMin, DistanceMax].
+    /// </summary>
+    public void AdjustDistance(float delta)
+    {
+        Distance = Math.Clamp(Distance + delta, DistanceMin, DistanceMax);
+    }
 }