feat(B-RL): Rate-Limiting Konsistenz — zentrale Policies für Auth/AI/Upload/Webhook

B-RL: Rate-Limiting auf zentrale check_rate_limit() umgestellt
- forgejo_error_reporter: In-Memory → zentrale Redis-Rate-Limit
- ai_proactive: eigene Redis-Logik → zentrale check_rate_limit()
- agent_runner: DB-basiertes Limit bleibt (zählt echte Ausführungen)
- RateLimitPolicy Enum (AUTH/AI/UPLOAD/WEBHOOK) + check_rate_limit_policy()
- 8 neue config.py Settings für Policy-Limits
- 12 Routes mit Policies versehen (login, password-reset, AI, uploads, webhooks)

Tests: 20 Tests in test_rate_limit_policies.py — alle grün
- Policies, check_rate_limit, reset, get_client_ip, forgejo, ai_proactive
- Keine Regression: 116 bestehende Tests grün

app/plugins/builtins/mail/routes.py

@@ -748,6 +748,13 @@ async def upload_attachment(
     user_id = uuid.UUID(current_user["user_id"])
     is_system_admin = current_user.get("is_system_admin", False)
 
+    # Rate limit — UPLOAD policy
+    from app.core.rate_limit import RateLimitPolicy, check_rate_limit_policy
+    await check_rate_limit_policy(
+        f"rate:upload:mail:{tenant_id}:{user_id}",
+        RateLimitPolicy.UPLOAD,
+    )
+
     # Read file content and check size
     content = await file.read()
     if len(content) > MAX_ATTACHMENT_SIZE: