Use free Telegram reactions for AI status (🤔/👍/👎)

Replace premium-only ⏳/✅/❌ with reactions available to all users:
🤔 while processing, 👍 on success, 👎 on error.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/commands/builtins.py

@@ -315,7 +315,7 @@ async def ai(ctx: "CommandContext") -> None:
         except Exception:
             pass
 
-    await _react("⏳")
+    await _react("🤔")
 
     try:
         response = await ai_service.generate(
@@ -328,9 +328,9 @@ async def ai(ctx: "CommandContext") -> None:
             ),
         )
     except (RuntimeError, ValueError) as exc:
-        await _react("❌")
+        await _react("👎")
         await ctx.reply(str(exc))
         return
 
-    await _react("✅")
+    await _react("👍")
     await _reply_long(ctx, response.text)