fix: use Box<dyn Write + Send> for cross-platform tracing writer

Replace platform-specific std::os::unix::io::FromRawFd with
Box<dyn std::io::Write + Send> return type. This compiles on
Windows, macOS, and Linux without unsafe code.

The closure now returns a boxed writer that is either:
- The cloned file handle (success case)
- A reopened file handle (clone failed)
- stderr (last resort, prevents panic)

crates/tui/src/runtime_log.rs

@@ -157,21 +157,23 @@ pub fn init() -> Result<TuiLogGuard> {
     let log_path_clone = log_path.clone();
     let subscriber = tracing_subscriber::registry().with(env_filter).with(
         fmt::layer()
-            .with_writer(move || {
+            .with_writer(move || -> Box<dyn std::io::Write + Send> {
                 // Clone the file handle for each write. If clone fails (fd exhaustion),
                 // fall back to reopening the same path, or ultimately stderr.
-                subscriber_file.try_clone().unwrap_or_else(|e| {
-                    tracing::warn!("Failed to clone log file handle: {e}, reopening");
-                    std::fs::OpenOptions::new()
-                        .create(true)
-                        .append(true)
-                        .open(&log_path_clone)
-                        .unwrap_or_else(|_| {
-                            // Last resort: wrap stderr as a File to prevent panic.
-                            use std::os::unix::io::FromRawFd;
-                            unsafe { std::fs::File::from_raw_fd(2) }
-                        })
-                })
+                match subscriber_file.try_clone() {
+                    Ok(f) => Box::new(f),
+                    Err(e) => {
+                        tracing::warn!("Failed to clone log file handle: {e}, reopening");
+                        match std::fs::OpenOptions::new()
+                            .create(true)
+                            .append(true)
+                            .open(&log_path_clone)
+                        {
+                            Ok(f) => Box::new(f),
+                            Err(_) => Box::new(std::io::stderr()),
+                        }
+                    }
+                }
             })
             .with_ansi(false)
             .with_target(true)