feat: add Android/Termux support by gating arboard dependency (#2895)

## Summary

This PR enables Codex to build and run on Android/Termux environments by
conditionally gating the arboard clipboard dependency for Android
targets.

## Key Changes

- **Android Compatibility**: Gate arboard dependency for Android targets
where clipboard access may be restricted
- **Build Fixes**: Add missing tempfile::Builder import for image
clipboard operations
- **Code Cleanup**: Remove unnecessary parentheses to resolve formatting
warnings

## Technical Details

### Clipboard Dependency Gating
- Uses conditional compilation to exclude arboard on Android targets
- Maintains full clipboard functionality on other platforms
- Prevents build failures on Android/Termux where system clipboard
access is limited

### Import Fixes
- Adds missing tempfile::Builder import that was causing compilation
errors
- Ensures image clipboard operations work correctly when clipboard is
available

## Platform Support

- ✅ **Linux/macOS/Windows**: Full clipboard functionality maintained
- ✅ **Android/Termux**: Builds successfully without clipboard dependency
- ✅ **Other Unix platforms**: Unchanged behavior

## Testing

- ✅ Builds successfully on Android/Termux
- ✅ Maintains clipboard functionality on supported platforms  
- ✅ No regression in existing functionality

This addresses the Android/Termux compatibility issues while keeping
clipboard functionality intact for platforms that support it.

codex-rs/tui/Cargo.toml

@@ -22,7 +22,6 @@ workspace = true
 
 [dependencies]
 anyhow = "1"
-arboard = "3"
 async-stream = "0.3.6"
 base64 = "0.22.1"
 chrono = { version = "0.4", features = ["serde"] }
@@ -93,6 +92,11 @@ pathdiff = "0.2"
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"
 
+# Clipboard support via `arboard` is not available on Android/Termux.
+# Only include it for non-Android targets so the crate builds on Android.
+[target.'cfg(not(target_os = "android"))'.dependencies]
+arboard = "3"
+
 
 [dev-dependencies]
 chrono = { version = "0.4", features = ["serde"] }