feat(#27): Gate B [07/10]: FastAPI health endpoint + app factory (H-1)

- App factory pattern (FUND-8): create_app() produces fresh app per test
- Logging config (structured, no secrets)
- Config validation: SLAB_AES_KEY required, WOO_BASE_URL HTTPS-only
- GET /api/health returns 200 {status: ok, version, woo_reachable: false}
- SQLite + alembic skeleton: full DATA-MODEL schema, initial migration
- API contract tests via httpx TestClient: 5 cases all green
  - test_returns_200, test_returns_ok_status, test_woo_reachable_false
  - test_response_shape, test_with_test_client_lifespan (FUND-9/10)

backend/alembic/env.py

@@ -0,0 +1,65 @@
+"""Alembic environment configuration.
+
+Sets up sys.path so that app packages are importable when running
+alembic from the backend directory.
+
+Alembic uses sync connections for migrations even with an async app.
+"""
+
+import os
+import sys
+
+# Ensure the backend root is on the path so app.* is importable
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from logging.config import fileConfig
+
+from alembic import context
+from sqlalchemy import engine_from_config, pool
+
+# Import models so that Base.metadata includes all tables
+from app.db.models import Base
+
+config = context.config
+
+fileConfig(config.config_file_name)
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode using sync engine."""
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection,
+            target_metadata=Base.metadata,
+            render_as_batch=True,
+        )
+        with context.begin_transaction():
+            context.run_migrations()
+
+    connectable.dispose()
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode."""
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(
+        url=url,
+        target_metadata=Base.metadata,
+        render_as_batch=True,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "batch"},
+    )
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()