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/data/app-data.ts

@@ -287,6 +287,14 @@ export const AppData = {
      * themselves to a reply; older ones are named.
      */
     BotReplyAttachmentMessages: 4,
+    /**
+     * Longest dictation the composer records before it stops on its own.
+     */
+    ComposerVoiceMaxMs: 5 * 60 * 1000,
+    /**
+     * Most of a bot message read aloud; the rest is cut.
+     */
+    SpeechMaxChars: 4000,
     /**
      * Largest picture a bot or a workspace can have.
      */

src/data/harness-prompts.ts

@@ -8,8 +8,6 @@ export const ReadImagePrompt = `Describe this image for someone who can't see it
 - For a screenshot, name the app or page, its state, and every control a user could click.
 - Don't guess at what you can't see. Plain text only, no preamble.`;
 
-export const TranscribeAudioPrompt = `Transcribe this audio exactly as spoken, in the language spoken. Output only the transcript: no preamble, no notes, no timestamps.`;
-
 /**
  * Added to the text model's prompt when a message part was read by another
  * harness, so it knows it is working from a description.