Add game mode manager with player-control and paint modes

Introduce an extensible game mode system toggled with Tab:
- Player Control: WASD movement with always-on mouse camera orbit
- Paint: player frozen, left-click paints, right-click holds to orbit

Add GameMode base class, GameModeManager, and the two concrete modes.
Refactor controlled scripts to expose clean state flags instead of
handling input themselves: ThirdPersonOrbitInput.LookMode,
PlayerCharacterController.ControlEnabled, MeshPainter.PaintingEnabled.

Also fix camera zoom: remove the obsolete /120 wheel normalization so
one scroll notch maps to one zoomSpeed step under the new Input System.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scenes/SampleScene.unity

@@ -152,16 +152,15 @@ MonoBehaviour:
   m_Script: {fileID: 11500000, guid: df129be8fadab79498bd429a59bb98e4, type: 3}
   m_Name: 
   m_EditorClassIdentifier: Assembly-CSharp::ThirdPersonOrbitInput
+  lookMode: 0
   horizontalSensitivity: 0.2
   verticalSensitivity: 0.15
   invertY: 0
-  toggleKey: 3
-  startInLookMode: 1
   enableZoom: 1
   zoomSpeed: 0.5
   minRadius: 1.5
   maxRadius: 8
-  lockCursorInLookMode: 1
+  manageCursor: 1
 --- !u!114 &172071432
 MonoBehaviour:
   m_ObjectHideFlags: 0
@@ -779,7 +778,7 @@ MonoBehaviour:
   m_EditorClassIdentifier: Assembly-CSharp::MeshPainter
   useGpu: 1
   brushColor: {r: 0, g: 0, b: 0, a: 1}
-  brushSize: 2
+  brushSize: 10
   textureSize: 1024
   baseColor: {r: 0.8, g: 0.8, b: 0.8, a: 1}
   paddingTexels: 2
@@ -1205,6 +1204,55 @@ MonoBehaviour:
   slideAcceleration: 20
   maxSlideSpeed: 8
   slideControl: 0.3
+--- !u!1 &1516578026
+GameObject:
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+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  serializedVersion: 6
+  m_Component:
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+  - component: {fileID: 1516578027}
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+  m_Name: GameManager
+  m_TagString: Untagged
+  m_Icon: {fileID: 0}
+  m_NavMeshLayer: 0
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+--- !u!114 &1516578027
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+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 1516578026}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 11500000, guid: 730466b26610d95498d22ab748d855a7, type: 3}
+  m_Name: 
+  m_EditorClassIdentifier: Assembly-CSharp::GameModeManager
+  player: {fileID: 1141039642}
+  cameraInput: {fileID: 172071431}
+  painter: {fileID: 682237521}
+  switchKey: 3
+  startModeIndex: 0
+--- !u!4 &1516578028
+Transform:
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+  m_LocalRotation: {x: 0, y: 0, z: 0, w: 1}
+  m_LocalPosition: {x: 0, y: 0, z: 0}
+  m_LocalScale: {x: 1, y: 1, z: 1}
+  m_ConstrainProportionsScale: 0
+  m_Children: []
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 --- !u!1 &1774267801
 GameObject:
   m_ObjectHideFlags: 0
@@ -1302,3 +1350,4 @@ SceneRoots:
   - {fileID: 963088882}
   - {fileID: 200502122}
   - {fileID: 172071436}
+  - {fileID: 1516578028}