fix(ci): graceful tailwind skip and add dx fmt check

build.rs no longer panics when bunx is unavailable, allowing
cargo clippy/test to run in CI without bun installed. Added
dx fmt --check to the format job for RSX formatting validation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

build.rs

@@ -1,8 +1,9 @@
-#[allow(clippy::expect_used)]
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     use std::process::Command;
     println!("cargo:rerun-if-changed=./styles/input.css");
-    Command::new("bunx")
+
+    // Tailwind build is optional - skip gracefully in CI or environments without bun
+    match Command::new("bunx")
         .args([
             "@tailwindcss/cli",
             "-i",
@@ -11,7 +12,15 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
             "./assets/tailwind.css",
         ])
         .status()
-        .expect("could not run tailwind");
+    {
+        Ok(status) if !status.success() => {
+            println!("cargo:warning=tailwind build exited with {status}, skipping CSS generation");
+        }
+        Err(e) => {
+            println!("cargo:warning=bunx not found ({e}), skipping tailwind CSS generation");
+        }
+        Ok(_) => {}
+    }
 
     Ok(())
 }