fix(transcription): resolve_language normalizes case-insensitive "en" match (T8.7, M4.2)

resolve_language(Some("EN"), false) was passed through unchanged instead of
being normalized to lowercase "en" - the English-only-model guard only fired
when the requested language *differed* from English, not when it matched with
different casing. Also fixes cargo fmt drift in mod.rs/npu.rs left over from
the M4.2 worktree (stopped mid-verification per session instruction before
running fmt).

src-tauri/src/transcription/mod.rs

@@ -76,7 +76,8 @@ fn resolve_language(requested: Option<&str>, multilingual: bool) -> Option<Strin
     match requested {
         None => None,
         Some(l) if l.eq_ignore_ascii_case("auto") => None,
-        Some(l) if !multilingual && !l.eq_ignore_ascii_case("en") => {
+        Some(l) if l.eq_ignore_ascii_case("en") => Some("en".to_string()),
+        Some(l) if !multilingual => {
             tracing::warn!(
                 "language '{l}' requested but the loaded model is English-only; forcing 'en'"
             );
@@ -399,8 +400,7 @@ mod tests {
             _ => BackendId::Intel, // use_gpu = true for any non-CPU backend
         };
         let t0 = std::time::Instant::now();
-        let transcriber =
-            WhisperTranscriber::load(Path::new(&model), backend, None).expect("load");
+        let transcriber = WhisperTranscriber::load(Path::new(&model), backend, None).expect("load");
         let load_ms = t0.elapsed().as_millis();
         let t1 = std::time::Instant::now();
         let segments = transcriber
@@ -474,7 +474,10 @@ mod tests {
         eprintln!("[spike] language={language} text={text:?}");
         assert!(!text.trim().is_empty(), "transcript was empty");
         // whisper.cpp reports back whichever language it actually decoded in.
-        assert_eq!(transcriber.detected_language().as_deref(), Some(language.as_str()));
+        assert_eq!(
+            transcriber.detected_language().as_deref(),
+            Some(language.as_str())
+        );
     }
 
     /// "Auto" acceptance spike (opt-in): confirms auto-detection actually
@@ -488,7 +491,11 @@ mod tests {
 
         let transcriber = WhisperTranscriber::load(Path::new(&model), BackendId::Cpu, None)
             .expect("load multilingual model");
-        assert_eq!(transcriber.effective_language(), None, "auto should stay unset");
+        assert_eq!(
+            transcriber.effective_language(),
+            None,
+            "auto should stay unset"
+        );
         assert_eq!(transcriber.detected_language(), None, "nothing decoded yet");
 
         transcriber

src-tauri/src/transcription/npu.rs

@@ -524,8 +524,7 @@ mod tests {
             _ => BackendId::Intel,
         };
         let t0 = std::time::Instant::now();
-        let t =
-            OnnxTranscriber::load(Path::new(&model_dir), backend, None).expect("load DirectML");
+        let t = OnnxTranscriber::load(Path::new(&model_dir), backend, None).expect("load DirectML");
         let load_ms = t0.elapsed().as_millis();
         let t1 = std::time::Instant::now();
         let segs = t.transcribe_file(Path::new(&wav)).expect("transcribe");