chore: PostgreSQL migration compatibility and infrastructure improvements

Database & Migrations:
- Update all Alembic migrations for PostgreSQL compatibility
- Remove SQLite-specific syntax (AUTOINCREMENT, etc.)
- Add database utility helpers for PostgreSQL operations
- Fix services to use PostgreSQL-compatible queries

Documentation:
- Add comprehensive Docker deployment guide
- Add production deployment documentation
- Add infrastructure architecture documentation
- Update database setup guide for PostgreSQL-only
- Expand troubleshooting guide

Architecture & Validation:
- Add migration.yaml rules for SQL compatibility checking
- Enhance validate_architecture.py with migration validation
- Update architecture rules to validate Alembic migrations

Development:
- Fix duplicate install-all target in Makefile
- Add Celery/Redis validation to install.py script
- Add docker-compose.test.yml for CI testing
- Add squash_migrations.py utility script
- Update tests for PostgreSQL compatibility
- Improve test fixtures in conftest.py

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/inventory_service.py

@@ -755,8 +755,17 @@ class InventoryService:
     ) -> AdminVendorsWithInventoryResponse:
         """Get list of vendors that have inventory entries (admin only)."""
         # noqa: SVC-005 - Admin function, intentionally cross-vendor
+        # Use subquery to avoid DISTINCT on JSON columns (PostgreSQL can't compare JSON)
+        vendor_ids_subquery = (
+            db.query(Inventory.vendor_id)
+            .distinct()
+            .subquery()
+        )
         vendors = (
-            db.query(Vendor).join(Inventory).distinct().order_by(Vendor.name).all()
+            db.query(Vendor)
+            .filter(Vendor.id.in_(db.query(vendor_ids_subquery.c.vendor_id)))
+            .order_by(Vendor.name)
+            .all()
         )
 
         return AdminVendorsWithInventoryResponse(