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/(partials)/harness-model-select.tsx

@@ -12,17 +12,20 @@ type Props = {
     models: HarnessModelOption[];
     model_id: number | null;
     provider_name?: string;
+    automatic: boolean;
     onChange: (model_id: number | null) => void;
 };
 
 /**
- * Searchable model picker: automatic, or any model that can do the job.
+ * Searchable model picker: automatic (or not available, for a harness
+ * without automatic picks), or any model that can do the job.
  */
 export default function HarnessModelSelect({
     id,
     models,
     model_id,
     provider_name,
+    automatic,
     onChange,
 }: Props) {
     return (
@@ -32,7 +35,7 @@ export default function HarnessModelSelect({
             label="Model"
             showLabel
             placeholder="Search models"
-            options={harnessModelSelectOptions({ models, model_id, provider_name })}
+            options={harnessModelSelectOptions({ models, model_id, provider_name, automatic })}
             defaultValues={[model_id ? String(model_id) : AutoModelValue]}
             changeHandler={(value) => {
                 const picked = Array.isArray(value) ? value[0] : value;