feat(app): add git diff viewer with dropdown menu and UI improvements

- Add git diff viewer screen to display local changes per agent
  - Parse git diff output into file sections with syntax highlighting
  - Horizontal scrolling for long diff lines (no text wrapping)
  - Request diff data on mount via new WebSocket messages

- Add dropdown menu to agent header
  - Three-dot menu button with "View Changes" option
  - Position menu below button using window-aware measurements
  - Account for safe area insets and orientation changes

- Implement server-side git operations
  - Add git_diff_request/response message types
  - Execute `git diff HEAD` in agent's working directory
  - Handle errors gracefully with proper error messages

- Update session context for git diff state
  - Add gitDiffs Map to store diff content per agent
  - Add requestGitDiff helper function
  - WebSocket handler for git_diff_response messages

- Improve agent input area layout
  - Move status bar inline with attachment button
  - Full-width text input above button row
  - Better spacing and visual hierarchy

- Simplify agent status bar to show only status dot

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/app/src/components/agent-status-bar.tsx

@@ -78,16 +78,13 @@ export function AgentStatusBar({ agentId }: AgentStatusBarProps) {
         </Pressable>
       )}
 
-      {/* Agent Status Indicator */}
-      <View style={styles.statusIndicator}>
-        <View
-          style={[
-            styles.statusDot,
-            { backgroundColor: getStatusColor(agent.status) },
-          ]}
-        />
-        <Text style={styles.statusText}>{getStatusLabel(agent.status)}</Text>
-      </View>
+      {/* Agent Status Indicator - just a dot */}
+      <View
+        style={[
+          styles.statusDot,
+          { backgroundColor: getStatusColor(agent.status) },
+        ]}
+      />
 
       {/* Mode selector modal */}
       <ModeSelectorModal
@@ -105,9 +102,6 @@ const styles = StyleSheet.create((theme) => ({
     flexDirection: "row",
     alignItems: "center",
     gap: theme.spacing[3],
-    paddingHorizontal: theme.spacing[4],
-    paddingTop: theme.spacing[2],
-    paddingBottom: theme.spacing[1],
   },
   modeBadge: {
     flexDirection: "row",