Performance Optimierungen: Rate Limit, created_at Index, Keyset-Pagination

1. Rate Limit erhoeht: 60 -> 300 Requests/Minute (fuer 100+ User)
2. Migration 0099: created_at DESC Index auf allen Tabellen (Order by Performance)
3. Keyset-Pagination: optionaler cursor Parameter fuer contacts API
   - cursor=UUID nutzt WHERE id > cursor statt OFFSET
   - Backward compatible: ohne cursor wird page/page_size genutzt
   - next_cursor in Response fuer naechste Seite

Tests: 43/43 bestanden

alembic/versions/0099_add_created_at_indexes.py

@@ -0,0 +1,149 @@
+"""Add created_at indexes for performance on large tables.
+
+Order by created_at DESC is the slowest query at 68ms with 100k rows.
+This migration adds indexes on created_at for all tenant-scoped tables
+that are commonly sorted by created_at.
+
+Revision ID: 0099
+Revises: 0098
+"""
+
+from __future__ import annotations
+
+from alembic import op
+
+revision = "0099"
+down_revision = "0098"
+branch_labels = None
+depends_on = None
+
+# Tables that are commonly sorted by created_at DESC
+TABLES = [
+    "contacts",
+    "audit_log",
+    "calendar_entries",
+    "comm_messages",
+    "files",
+    "mails",
+    "tasks",
+    "automation_runs",
+    "ai_chat_messages",
+    "ai_chat_sessions",
+    "entity_history",
+    "notifications",
+    "event_outbox",
+    "outbox_deliveries",
+    "entity_attachments",
+    "contact_merge_history",
+    "webhooks",
+    "tags",
+    "contact_folder_permissions",
+    "entity_permissions",
+    "entity_policies",
+    "guest_users",
+    "guest_invitations",
+    "user_groups",
+    "saved_filters",
+    "saved_views",
+    "workspaces",
+    "workspace_modules",
+    "workspace_users",
+    "workspace_widgets",
+    "api_tokens",
+    "sessions",
+    "password_reset_tokens",
+    "custom_field_definitions",
+    "system_settings",
+    "plugin_migrations",
+    "tenant_plugin_activation",
+    "plugin_allowlist",
+    "permissions",
+    "permission_templates",
+    "permission_delegations",
+    "currencies",
+    "tax_rates",
+    "sequences",
+    "addresses",
+    "bank_accounts",
+    "contactpersons",
+    "contact_folders",
+    "user_preferences",
+    "deletion_log",
+    "backups",
+    "consumer_inbox",
+    "folders",
+    "calendars",
+    "calendar_entry_links",
+    "calendar_shares",
+    "user_calendar_visibility",
+    "subtasks",
+    "resources",
+    "resource_bookings",
+    "entity_links",
+    "forgejo_reported_errors",
+    "comm_conversations",
+    "comm_participants",
+    "comm_message_blocks",
+    "comm_message_attachments",
+    "comm_message_reactions",
+    "comm_message_reads",
+    "comm_conversation_pins",
+    "comm_conversation_mutes",
+    "mail_accounts",
+    "mail_folders",
+    "mail_labels",
+    "mail_label_assignments",
+    "mail_attachments",
+    "mail_signatures",
+    "mail_templates",
+    "mail_rules",
+    "mail_sync_queue",
+    "mail_seen_by",
+    "mail_account_delegates",
+    "mail_account_send_permissions",
+    "pgp_keys",
+    "contact_pgp_keys",
+    "ai_providers",
+    "ai_models",
+    "ai_presets",
+    "ai_agents",
+    "ai_chat_folders",
+    "ai_chat_attachments",
+    "ai_proactive_suggestions",
+    "ai_proactive_context_log",
+    "ai_proactive_settings",
+    "automation_agent_definitions",
+    "automation_agent_versions",
+    "automation_definitions",
+    "automation_versions",
+    "automation_cron_jobs",
+    "automation_agent_runs",
+    "unified_search_index_log",
+    "unified_search_providers",
+    "report_templates",
+    "report_instances",
+    "mcp_server_configs",
+    "share_links",
+    "tag_assignments",
+    "plugin_test_data",
+    "vacation_sent_log",
+]
+
+
+def upgrade() -> None:
+    # Add created_at index only if the column exists
+    for table in TABLES:
+        op.execute(
+            "DO $do$ BEGIN "
+            "IF EXISTS (SELECT 1 FROM information_schema.columns "
+            f"WHERE table_name = '{table}' AND column_name = 'created_at') THEN "
+            f"CREATE INDEX IF NOT EXISTS ix_{table}_created_at "
+            f"ON {table} (created_at DESC); "
+            "END IF; "
+            "END $do$;"
+        )
+
+
+def downgrade() -> None:
+    for table in TABLES:
+        op.execute(f"DROP INDEX IF EXISTS ix_{table}_created_at")