feat: auto-run SQL migrations on backend startup

Adds migration_runner.py that executes pending migrations from
migrations/ directory when backend-compliance starts. Tracks applied
migrations in _migration_history table.

Handles existing databases: detects if tables from migrations 001-045
already exist and seeds the history table accordingly, so only new
migrations (046+) are applied.

Skippable via SKIP_MIGRATIONS=true env var.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend-compliance/main.py

@@ -7,10 +7,15 @@ Provides: Compliance Framework, Consent Admin, DSR, GDPR Export.
 Runs on port 8002 with DB search_path=compliance,core,public.
 """
 
+import logging
 import os
+from contextlib import asynccontextmanager
+
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
+logger = logging.getLogger(__name__)
+
 # Compliance-specific API routers
 from consent_api import router as consent_router
 from consent_admin_api import router as consent_admin_router
@@ -36,10 +41,23 @@ from middleware import (
     SecurityHeadersMiddleware,
 )
 
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Run migrations on startup."""
+    from migration_runner import run_migrations
+    try:
+        run_migrations()
+        logger.info("Database migrations completed")
+    except Exception as e:
+        logger.error("Migration failed: %s — backend starting anyway", e)
+    yield
+
+
 app = FastAPI(
     title="BreakPilot Compliance Backend",
     description="GDPR/DSGVO Compliance, Consent Management, Data Subject Requests, and Regulatory Compliance Framework",
     version="1.0.0",
+    lifespan=lifespan,
 )
 
 # --- CORS ---