feat: show budget limit message with MatrixHost link instead of generic error

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bot.py

@@ -15,6 +15,7 @@ import docx
 import fitz  # pymupdf
 import httpx
 from openai import AsyncOpenAI
+import openai as _openai
 from olm import sas as olm_sas
 import olm.pk
 import canonicaljson
@@ -3298,6 +3299,20 @@ class Bot:
                     await self._auto_rename_room(room, user_message, reply)
 
             return reply
+        except _openai.APIStatusError as e:
+            body = getattr(e, "body", None) or {}
+            msg = body.get("message", "") if isinstance(body, dict) else str(body)
+            if "BudgetGuard" in msg or "exceed budget" in msg:
+                logger.warning("LLM budget exceeded: %s", msg)
+                portal = PORTAL_URL.rstrip("/")
+                await self._send_text(
+                    room.room_id,
+                    f"⚠️ AI budget limit reached. Please check your plan at {portal}/settings/billing",
+                )
+            else:
+                logger.exception("LLM API error")
+                await self._send_text(room.room_id, "Sorry, I couldn't generate a response.")
+            return None
         except Exception:
             logger.exception("LLM call failed")
             await self._send_text(room.room_id, "Sorry, I couldn't generate a response.")