fix: settle silent-only cases to Empty oneliner state

Introduce `TranscriptState { Pending, Silent, Content }` in
doctate-common as the canonical three-way state of a recording's
`.transcript.txt` sidecar. Previously each call-site projected the
raw `Option<String>` / `.exists()` onto its own 2-state view and the
projections disagreed: the UI treated a 0-byte silent transcript like
`Content` while the oneliner worker treated it like `Pending`,
leaving silent-only cases stuck on "generiere Titel …" forever with
no persisted oneliner.json.

`update_oneliner` now settles a silent-only case to
`OnelinerState::Empty` when no `Content` transcript exists and no
recording is still `Pending`, so the UI resolves to "unbenannt" and
recovery treats it as terminal.

Single reader: `paths::read_transcript_state`. All call-sites
(scan_recordings, compute_oneliner_display, has_pending_recordings,
all_transcripts_joined, read_recordings, enqueue_pending_for_user,
scan_m4as, cases_needing_oneliner_in, case_recordings.html) go
through the same typed abstraction and must handle `Silent` via
exhaustive match.

Regression tests:
- silent_case_empty_test: heal path settles silent-only case to
  Empty without calling Ollama
- case_page_silent_only_shows_empty_not_generating: UI renders
  "unbenannt", not "generiere Titel …"

server/tests/case_page_test.rs

@@ -338,6 +338,45 @@ async fn case_page_uses_oneliner_as_h1_when_present() {
     );
 }
 
+/// A case with only silent recordings (empty 0-byte transcript) and a
+/// persisted `OnelinerState::Empty` must render the "unbenannt" variant
+/// of the oneliner, never "generiere Titel …". Regression guard for
+/// the bug where the UI's `compute_oneliner_display` collapsed
+/// `TranscriptState::Silent` onto "transcribed" and then chose
+/// `Generating` because no state was persisted — the combination left
+/// cases stuck on "generiere Titel …" forever.
+#[tokio::test]
+async fn case_page_silent_only_shows_empty_not_generating() {
+    let config = config_with_llm(unique_tmp("cp-silent"));
+    let case_id = "33333333-3333-3333-3333-333333333333";
+    let case_dir = seed_case(&config.data_path, "dr_a", case_id);
+    // `Some("")` produces a 0-byte transcript sidecar — the whisper-as-
+    // silence output. Combined with `OnelinerState::Empty`, this is the
+    // terminal shape of a silent-only case after the fix.
+    seed_recording(&case_dir, "10-00-00", Some(""));
+    seed_oneliner_state(
+        &case_dir,
+        &OnelinerState::Empty {
+            generated_at: "2026-04-21T11:00:00Z".into(),
+        },
+    );
+
+    let app = doctate_server::create_router(config);
+    let cookie = login(app.clone(), "dr_a").await;
+
+    let resp = app.oneshot(get_page(case_id, &cookie, "")).await.unwrap();
+    let body = body_string(resp).await;
+
+    assert!(
+        !body.contains("generiere Titel"),
+        "silent-only case must not be stuck on 'generiere Titel …'"
+    );
+    assert!(
+        body.contains("unbenannt"),
+        "expected oneliner to render as 'unbenannt' for Empty state"
+    );
+}
+
 #[tokio::test]
 async fn case_page_falls_back_to_generic_title_for_empty_state() {
     // An `Empty` state (LLM deliberately returned no medical content) is