Add user-configurable TTS pronunciation overrides

A JSON map (TTS_PRONUNCIATIONS_PATH, default tts_pronunciations.json)
rewrites mispronounced words — place names, initialisms, dotted
abbreviations — to phonetic spellings before synthesis, applied after
markdown cleanup in both /tts/speech paths. Whole-word smartcase
matching (lowercase keys match any casing, uppercase keys exact),
longest key wins, hot-reloaded on mtime change with last-good fallback
on parse errors. See tts_pronunciations.example.json.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/ai/tts.rs

@@ -254,6 +254,14 @@ fn clean_for_tts(input: &str) -> String {
     s.trim().to_string()
 }
 
+/// Full text-preparation pipeline for synthesis: markdown/emoji cleanup, then
+/// the user's pronunciation overrides (see [`crate::ai::pronunciation`]) on
+/// the resulting plain text — after cleanup so word boundaries aren't
+/// obscured by `**WSL**`-style markup.
+fn prepare_for_tts(input: &str) -> String {
+    crate::ai::pronunciation::apply_pronunciations(&clean_for_tts(input))
+}
+
 /// Decode an audio/video file to mono 24 kHz WAV via ffmpeg, returning the WAV
 /// bytes. Chatterbox validates the reference clip by file *extension* and
 /// rejects several formats (e.g. `.aac`, `.opus`), so we always normalize to
@@ -337,7 +345,7 @@ pub async fn tts_speech_handler(
     let parent_context = extract_context_from_request(&http_request);
     let mut span = global_tracer().start_with_context("http.tts.speech", &parent_context);
 
-    let text = clean_for_tts(&req.text);
+    let text = prepare_for_tts(&req.text);
     if text.is_empty() {
         span.set_status(Status::error("text is required"));
         return HttpResponse::BadRequest().json(json!({ "error": "text is required" }));
@@ -435,7 +443,7 @@ pub async fn create_speech_job_handler(
     let mut span =
         global_tracer().start_with_context("http.tts.speech_job.create", &parent_context);
 
-    let text = clean_for_tts(&req.text);
+    let text = prepare_for_tts(&req.text);
     if text.is_empty() {
         span.set_status(Status::error("text is required"));
         return HttpResponse::BadRequest().json(json!({ "error": "text is required" }));