Add dictation and streamed read-aloud to the chat

- A mic in the composer records, transcribes with the bot's
  transcription model (api/admin/bots/transcribe) and writes the text
  into the input at the cursor to edit before sending. Escape cancels;
  recordings aren't stored.
- Every bot message has a read-aloud button that plays
  GET api/admin/bots/speak-message, streamed from the provider as the
  audio is made, so it starts in a couple of seconds. One message plays
  at a time; only the user's own sessions can be read.
- Both buttons stay visible but disabled while the bot has no model for
  them (bot_voice page prop).
- Transcription and speech no longer pick free models automatically:
  they're not available until a model is picked, and Settings says so.
  Transcription lists speech-to-text models only, so the chat-model
  transcript path and its missing-audio check are gone.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/pages/admin/settings/models/(utils)/harness-model-select-options.ts

@@ -13,24 +13,33 @@ type Params = {
      * The picked provider's name; undefined for any provider.
      */
     provider_name?: string;
+    /**
+     * False: there's no automatic pick, so the empty choice reads "Not
+     * available".
+     */
+    automatic: boolean;
 };
 
 /**
  * The model picker's options: automatic (the best free model, on the
  * picked provider if there is one), then every model that can do the job
- * (free ones first, as the server sorts them).
+ * (free ones first, as the server sorts them). A harness without
+ * automatic picks starts with "Not available" instead.
  */
 export default function harnessModelSelectOptions({
     models,
     model_id,
     provider_name,
+    automatic,
 }: Params): TWUISelectOptionObject[] {
     const has_free = models.some((model) => model.free);
 
     return [
         {
             value: AutoModelValue,
-            title: provider_name
+            title: !automatic
+                ? "Not available (pick a model to turn it on)"
+                : provider_name
                 ? has_free
                     ? `Automatic (best free model on ${provider_name})`
                     : `Automatic (no free models on ${provider_name}: pick one)`