feat: Web-Such-Budget pro Nutzer/Tag

Neue Tabelle web_search_usage + Store-Zaehler (web_search_count /
add_web_search_usage, kaskadiert in delete_user). Pro-Nutzer-Limit
web_search_daily_limit (Pref > global; 0 = unbegrenzt) in quota.py
(web_search_within_budget). ws.py: Gate vor _resolve (Budget aufgebraucht ->
Web-Suche fuer den Turn aus) + Zaehlung nach dem Turn (trace.web_searches,
gezaehlt im Orchestrator je on_citations). Admin: Feld + UI-Eingabe.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/quota.py

@@ -40,3 +40,31 @@ def enforce_quota(user, store, cfg=None) -> None:
 def record_usage(user, store, units: int = 0) -> None:
     store.add_usage(user.id, units)
     metrics.inc("turns_total")
+
+
+def web_search_limit(user, cfg=None) -> int:
+    """Max. Web-Suchen pro Tag fuer diesen Nutzer (Pref > global; 0 = unbegrenzt)."""
+    if cfg is None:
+        from app.runtime_config import runtime_settings
+        cfg = runtime_settings
+    pref = user.prefs.get("web_search_daily_limit") if user and user.prefs else None
+    if pref is not None:
+        try:
+            return int(pref)
+        except (TypeError, ValueError):
+            pass
+    return cfg.web_search_daily_limit
+
+
+def web_search_within_budget(user, store, cfg=None) -> bool:
+    """Darf der Nutzer heute noch eine Web-Suche ausloesen? (Limit 0 = unbegrenzt)."""
+    limit = web_search_limit(user, cfg)
+    if not limit or limit <= 0:
+        return True
+    return store.web_search_count(user.id) < limit
+
+
+def record_web_search(user, store, n: int = 1) -> None:
+    """Zaehlt n tatsaechlich ausgefuehrte Web-Suchen fuer den Nutzer."""
+    if n and n > 0 and user is not None:
+        store.add_web_search_usage(user.id, n)