Phase 0 Complete: Tasks 0.7-0.20

- 0.7: UI-Design-Richtlinien (docs/ui-design-guidelines.md, 535 lines)
- 0.8: Theme-Customization Backend (4 theme fields, migration 0023)
- 0.9: Theme-Customization Frontend (SettingsTheme.tsx, themeStore.ts, live preview)
- 0.10: RBAC-Audit (4 plugins secured, 53 routes with require_permission)
- 0.11: LiteLLM-Cleanup (llm_client.py migrated from httpx to litellm)
- 0.12: KI-Agent-Framework docs (plugin-development-guide.md, agent_capabilities field)
- 0.13: Heartbeat configurable (ProactiveSettings, migration 0024, frontend UI)
- 0.14: Unified Search Field-Level RBAC (resolve_permissions + filter_fields_by_permission)
- 0.15: Undo/History-System (EntityHistory model, service, routes, migration 0025, HistoryViewer)
- 0.16: Storage Backend (LocalStorage + S3Storage, DMS/attachments/mail updated)
- 0.17: Import/Export unified Contact fields (firstname, surname, email_1, phone_1)
- 0.18: .gitignore & Config-Cleanup (webui→frontend, python-jose removed, .env untracked)
- 0.19: Mail-Salt Security-Fix (per-account random salt, migration 0026)
- 0.20: AGPL replaced (PyMuPDF→pypdf, OnlyOffice→Collabora, LICENSE + THIRD_PARTY_LICENSES.md)

alembic/versions/0025_entity_history.py

@@ -0,0 +1,57 @@
+"""Entity history table for undo/restore functionality.
+
+Revision ID: 0025_entity_history
+Revises: 0024_heartbeat_config
+Create Date: 2026-07-23
+"""
+
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+revision: str = "0025_entity_history"
+down_revision: Union[str, None] = "0024_heartbeat_config"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "entity_history",
+        sa.Column("id", postgresql.UUID(as_uuid=True), primary_key=True),
+        sa.Column("tenant_id", postgresql.UUID(as_uuid=True), sa.ForeignKey("tenants.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("user_id", postgresql.UUID(as_uuid=True), sa.ForeignKey("users.id", ondelete="SET NULL"), nullable=True),
+        sa.Column("entity_type", sa.String(50), nullable=False),
+        sa.Column("entity_id", postgresql.UUID(as_uuid=True), nullable=False),
+        sa.Column("action", sa.String(20), nullable=False),
+        sa.Column("snapshot_before", postgresql.JSONB, nullable=True),
+        sa.Column("snapshot_after", postgresql.JSONB, nullable=True),
+        sa.Column("changes", postgresql.JSONB, nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("updated_at", sa.DateTime(timezone=True), nullable=False, server_default=sa.func.now()),
+        sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+    )
+    op.create_index("ix_entity_history_tenant_id", "entity_history", ["tenant_id"])
+    op.create_index("ix_entity_history_entity_type", "entity_history", ["entity_type"])
+    op.create_index("ix_entity_history_entity_id", "entity_history", ["entity_id"])
+    op.create_index("ix_entity_history_user_id", "entity_history", ["user_id"])
+    op.create_index("ix_entity_history_created_at", "entity_history", ["created_at"])
+    op.create_index(
+        "ix_entity_history_tenant_entity",
+        "entity_history",
+        ["tenant_id", "entity_type", "entity_id", "created_at"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_index("ix_entity_history_tenant_entity", table_name="entity_history")
+    op.drop_index("ix_entity_history_created_at", table_name="entity_history")
+    op.drop_index("ix_entity_history_user_id", table_name="entity_history")
+    op.drop_index("ix_entity_history_entity_id", table_name="entity_history")
+    op.drop_index("ix_entity_history_entity_type", table_name="entity_history")
+    op.drop_index("ix_entity_history_tenant_id", table_name="entity_history")
+    op.drop_table("entity_history")