fix: resolve agent crash and expand settings sheet

- Move task_dir assignment before VoiceAssistant construction in
  handle_job; UnboundLocalError was crashing every agent job before it
  joined the room, leaving the UI stuck on 'Opening a secure room'
- Make settings sheet full-window height (100dvh) to match tasks panel

agent/agent.py

@@ -652,6 +652,10 @@ async def handle_job(ctx: JobContext) -> None:
         return
     logger.info("Resolved voice user %s", user_id)
 
+    # Every room gets a private event directory. This prevents concurrent or
+    # reconnecting sessions from consuming and announcing each other's tasks.
+    task_dir = f"/tmp/tasks/{ctx.room.name}"
+
     # Azure STT — streaming, reads AZURE_SPEECH_KEY / AZURE_SPEECH_REGION from env
     stt = azure.STT(
         speech_key=AZURE_KEY,
@@ -799,9 +803,6 @@ async def handle_job(ctx: JobContext) -> None:
         logger.info("user state -> %s", ev.new_state)
 
     # ── Background task events → UI and spoken result ──────────────────────
-    # Every room gets a private event directory. This prevents concurrent or
-    # reconnecting sessions from consuming and announcing each other's tasks.
-    task_dir = f"/tmp/tasks/{ctx.room.name}"
     try:
         from agent.task_registry import TaskRegistry
     except ImportError: