Add OnelinerState::Manual variant

This commit introduces a new `Manual` variant to the `OnelinerState`
enum, allowing for manual overrides of the oneliner text. This change
affects the client and server components to handle and display this new
state.

A `OnelinerOverrideRequest` struct is also added for API requests to set
manual oneliners. New tests are included to ensure the `Manual` variant
serializes and deserializes correctly.

The `compute_oneliner_display` function in
`server/src/routes/user_web.rs` is updated to treat `Manual` states the
same as `Ready` states for display purposes. The
`cases_needing_oneliner_in` function in
`server/src/transcribe/recovery.rs` is updated to not retry cases that
are in a `Manual` state.

server/src/paths.rs

@@ -83,6 +83,21 @@ pub async fn read_oneliner_state(
     (Some(state), mtime)
 }
 
+/// Write `state` atomically to `case_dir/oneliner.json` via
+/// `write(tmp) + rename(tmp, final)`. Rename is atomic within a single
+/// filesystem, so concurrent readers never see a half-serialized JSON
+/// document.
+pub async fn write_oneliner_state(
+    case_dir: &Path,
+    state: &OnelinerState,
+) -> std::io::Result<()> {
+    let final_path = case_dir.join(ONELINER_FILENAME);
+    let tmp_path = case_dir.join(format!("{ONELINER_FILENAME}.tmp"));
+    let payload = serde_json::to_vec(state).expect("OnelinerState is infallibly serializable");
+    tokio::fs::write(&tmp_path, &payload).await?;
+    tokio::fs::rename(&tmp_path, &final_path).await
+}
+
 /// Load the `.transcript.txt` sidecar for a recording as a
 /// [`TranscriptState`].
 ///