UI: 增大摇杆尺寸至180dp；视频全屏延展（ZOOM模式）并加入缩放模式设置项

- 左右摇杆 Modifier.size 140dp -> 180dp (MainScreen.kt)
- RtspVideoPlayer 新增 resizeMode: VideoResizeMode 参数，默认 ZOOM
- 新增 VideoResizeMode 枚举 (FIT/ZOOM/FILL) 及 Media3 常量映射
- 设置界面新增"视频缩放模式"下拉选项，持久化到 DataStore
- AGENTS.md 更新已完成项和配置项表格

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

.idea/deploymentTargetSelector.xml

@@ -4,10 +4,10 @@
     <selectionStates>
       <SelectionState runConfigName="app">
         <option name="selectionMode" value="DROPDOWN" />
-        <DropdownSelection timestamp="2026-07-17T08:19:04.728150600Z">
+        <DropdownSelection timestamp="2026-07-17T11:46:26.977945400Z">
           <Target type="DEFAULT_BOOT">
             <handle>
-              <DeviceId pluginId="Default" identifier="serial=192.168.137.221:5555;connection=f0ff1c4d" />
+              <DeviceId pluginId="LocalEmulator" identifier="path=C:\Users\evan\.android\avd\Medium_Phone.avd" />
             </handle>
           </Target>
         </DropdownSelection>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>