Refactor ETag generation for oneliners API

Remove the per-user oneliner watermark, which was previously used to
generate ETags for the `/api/oneliners` endpoint. The watermark was
intended to track the last successful oneliner write for each user.

The ETag generation has been refactored to use a deterministic FNV-1a
hash. This hash is computed over a sorted list of tuples containing
`(case_id, last_recording_at_ns, oneliner_mtime_ns)` for all visible
cases. This approach ensures that the ETag changes whenever any
listen-relevant file system modification occurs, such as a new
recording, oneliner regeneration, soft-delete, undo, or
upload-auto-reopen. This new method is more robust and avoids the
complexity of managing per-user state.

The `OnelinerWatermark` type alias and its associated logic have been
removed from `AppState` and the relevant modules (`transcribe::worker`,
`transcribe::recovery`, `routes::oneliners`, `main`). New integration
tests have been added to verify that various delete operations (single
delete, undo delete, bulk delete) correctly trigger an ETag update,
ensuring cache invalidation.

server/src/transcribe/worker.rs

@@ -2,13 +2,12 @@ use std::path::Path;
 use std::sync::Arc;
 use std::time::Duration;
 
-use time::OffsetDateTime;
 use tracing::{error, info, warn};
 
 use super::{ffmpeg, ollama, whisper, TranscribeReceiver};
 use crate::config::{Config, WhisperUserSettings};
 use crate::gazetteer::Gazetteer;
-use crate::{BusyGuard, OnelinerWatermark, WorkerBusy};
+use crate::{BusyGuard, WorkerBusy};
 
 const ONELINER_TIMEOUT: Duration = Duration::from_secs(60);
 
@@ -20,7 +19,6 @@ pub async fn run(
     client: reqwest::Client,
     worker_busy: WorkerBusy,
     vocab: Arc<Gazetteer>,
-    watermark: OnelinerWatermark,
 ) {
     info!("Transcription worker started");
     let timeout = Duration::from_secs(config.whisper_timeout_seconds);
@@ -90,7 +88,7 @@ pub async fn run(
         if let Some(case_dir) = audio_path.parent()
             && !has_pending_recordings(case_dir).await
         {
-            update_oneliner(case_dir, &job.user_slug, &client, &config, &vocab, &watermark).await;
+            update_oneliner(case_dir, &job.user_slug, &client, &config, &vocab).await;
         }
     }
 
@@ -133,7 +131,6 @@ pub(crate) async fn update_oneliner(
     client: &reqwest::Client,
     config: &Config,
     vocab: &Gazetteer,
-    watermark: &OnelinerWatermark,
 ) {
     let path = case_dir.join("oneliner.txt");
 
@@ -157,13 +154,12 @@ pub(crate) async fn update_oneliner(
             if let Err(e) = tokio::fs::write(&path, &line).await {
                 error!(path = %path.display(), error = %e, "writing oneliner failed");
             } else {
-                info!(path = %path.display(), chars = line.chars().count(), "Oneliner updated");
-                // Bump the per-user watermark so the next `/api/oneliners`
-                // poll sees a fresh ETag and fetches the new content.
-                watermark
-                    .write()
-                    .await
-                    .insert(user_slug.to_string(), OffsetDateTime::now_utc());
+                info!(
+                    user = %user_slug,
+                    path = %path.display(),
+                    chars = line.chars().count(),
+                    "Oneliner updated"
+                );
             }
         }
         Err(e) => {