feat: gray out unsupported profiles instead of filtering, auto-switch engine on selection

- Show all voice profiles with unsupported ones grayed out (opacity) instead of hidden
- Clicking a grayed-out profile selects it and auto-switches the engine to a compatible one
- Sort supported profiles first, with info tip about compatibility at the bottom
- Scroll to selected profile after engine/sort changes with safe margin
- Fix engine desync on tab navigation by initializing form engine from store

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

backend/routes/profiles.py

@@ -4,6 +4,7 @@ import io
 import json as _json
 import logging
 import tempfile
+from datetime import datetime
 from pathlib import Path
 
 from fastapi import APIRouter, Depends, File, Form, HTTPException, UploadFile