feat(preview): floating transcription overlay with listening→live→cleanup→final phases

Ported the best bits of OpenWhispr's TranscriptionPreviewOverlay into Kon's
window conventions. Off by default — toggle in Settings → Output → "Floating
preview when Kon is unfocused". Opens only when the main window isn't
focused at the start of a recording, so it never adds noise when the user
can already see the transcript in the main surface.

Phase state machine (src/routes/preview/+page.svelte):
- listening — pulsing dot, no text yet
- live      — animated bars + streaming raw Whisper output
- cleanup   — accent bars while the LLM cleanup pass runs
- final     — checkmark + formatted text + 4s auto-hide

Data plumbing: raw segment text is captured before post_process_segments in
live.rs (new raw_text field on LiveResultMessage) and in transcription.rs
(new raw_text in the transcription-result payload). DictationPage forwards
raw_text to the overlay via Tauri global events — preview-listening on
start, preview-append per chunk, preview-cleanup before the LLM pass,
preview-final with the formatted text, preview-hide when a run produced no
transcript (empty recording / cancel).

Window is always_on_top, skip_taskbar, focused=false so it never steals
focus from whatever the user is dictating into. open_preview_window shows
an existing hidden preview or builds it fresh; close_preview_window hides
without destroying so the next open is instant.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src-tauri/src/commands/transcription.rs

@@ -188,6 +188,7 @@ pub async fn transcribe_pcm(
     let dictionary_terms = profile_terms.clone();
 
     let mut segments: Vec<Segment> = timed.transcript.segments().to_vec();
+    let raw_text = join_segment_text(&segments);
     post_process_segments(
         &mut segments,
         &PostProcessOptions {
@@ -209,6 +210,7 @@ pub async fn transcribe_pcm(
             "duration": timed.transcript.duration(),
             "chunk_id": chunk_id,
             "inference_ms": timed.inference_ms,
+            "raw_text": raw_text,
         }),
     )
     .map_err(|e| format!("Failed to emit result: {e}"))?;
@@ -216,6 +218,15 @@ pub async fn transcribe_pcm(
     Ok(())
 }
 
+fn join_segment_text(segments: &[Segment]) -> String {
+    segments
+        .iter()
+        .map(|segment| segment.text.trim())
+        .filter(|segment| !segment.is_empty())
+        .collect::<Vec<_>>()
+        .join(" ")
+}
+
 /// Transcribe an audio file by path. Decodes, resamples to 16kHz, runs Whisper.
 #[tauri::command]
 pub async fn transcribe_file(
@@ -279,6 +290,7 @@ pub async fn transcribe_file(
     let dictionary_terms = profile_terms.clone();
 
     let mut segments: Vec<Segment> = timed.transcript.segments().to_vec();
+    let raw_text = join_segment_text(&segments);
     post_process_segments(
         &mut segments,
         &PostProcessOptions {
@@ -298,6 +310,7 @@ pub async fn transcribe_file(
         "language": timed.transcript.language(),
         "duration": timed.transcript.duration(),
         "inference_ms": timed.inference_ms,
+        "raw_text": raw_text,
     }))
 }
 
@@ -344,6 +357,7 @@ pub async fn transcribe_pcm_parakeet(
     let dictionary_terms = profile_terms.clone();
 
     let mut segments: Vec<Segment> = timed.transcript.segments().to_vec();
+    let raw_text = join_segment_text(&segments);
     post_process_segments(
         &mut segments,
         &PostProcessOptions {
@@ -365,6 +379,7 @@ pub async fn transcribe_pcm_parakeet(
             "duration": timed.transcript.duration(),
             "chunk_id": chunk_id,
             "inference_ms": timed.inference_ms,
+            "raw_text": raw_text,
         }),
     )
     .map_err(|e| format!("Failed to emit result: {e}"))?;