refactor(migrations): squash 75 migrations into 12 per-module initial migrations

The old migration chain was broken (downgrade path through vendor->merchant
rename made rollbacks impossible). This squashes everything into fresh
per-module migrations with zero schema drift, verified by autogenerate.

Changes:
- Replace 75 accumulated migrations with 12 per-module initial migrations
  (core, billing, catalog, marketplace, cms, customers, orders, inventory,
  cart, messaging, loyalty, dev_tools) in a linear chain
- Fix make db-reset to use SQL DROP SCHEMA instead of alembic downgrade base
- Enable migration autodiscovery for all modules (migrations_path in definitions)
- Rewrite alembic/env.py to import all 75 model tables across 13 modules
- Fix AdminNotification import (was incorrectly from tenancy, now from messaging)
- Update squash_migrations.py to handle all module migration directories

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

scripts/squash_migrations.py

@@ -2,7 +2,7 @@
 """
 Migration Squash Script
 
-This script squashes all existing migrations into a single initial migration.
+This script squashes all existing migrations into fresh per-module initial migrations.
 Run this after setting up PostgreSQL to simplify the migration history.
 
 Prerequisites:
@@ -13,13 +13,13 @@ Usage:
     python scripts/squash_migrations.py
 
 What this script does:
-1. Backs up existing migrations to alembic/versions_backup_YYYYMMDD/
+1. Backs up existing migrations from all version_locations to a timestamped backup
 2. Creates a fresh initial migration from current models
 3. Stamps the database as being at the new migration
 
 After running:
-1. Review the new migration in alembic/versions/
-2. Test with: make migrate-up (on a fresh database)
+1. Review the new migration files
+2. Test with: make db-reset (drops schema, runs all migrations, seeds data)
 3. If satisfied, delete the backup directory
 """
 
@@ -36,6 +36,22 @@ sys.path.insert(0, str(project_root))
 
 VERSIONS_DIR = project_root / "alembic" / "versions"
 
+# All migration version directories (core + modules)
+MODULE_MIGRATION_DIRS = [
+    project_root / "alembic" / "versions",
+    project_root / "app" / "modules" / "billing" / "migrations" / "versions",
+    project_root / "app" / "modules" / "cart" / "migrations" / "versions",
+    project_root / "app" / "modules" / "catalog" / "migrations" / "versions",
+    project_root / "app" / "modules" / "cms" / "migrations" / "versions",
+    project_root / "app" / "modules" / "customers" / "migrations" / "versions",
+    project_root / "app" / "modules" / "dev_tools" / "migrations" / "versions",
+    project_root / "app" / "modules" / "inventory" / "migrations" / "versions",
+    project_root / "app" / "modules" / "loyalty" / "migrations" / "versions",
+    project_root / "app" / "modules" / "marketplace" / "migrations" / "versions",
+    project_root / "app" / "modules" / "messaging" / "migrations" / "versions",
+    project_root / "app" / "modules" / "orders" / "migrations" / "versions",
+]
+
 
 def check_prerequisites():
     """Verify PostgreSQL is configured."""
@@ -53,28 +69,42 @@ def check_prerequisites():
 
 
 def backup_migrations():
-    """Backup existing migrations."""
+    """Backup existing migrations from all version locations."""
     timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
     backup_dir = project_root / "alembic" / f"versions_backup_{timestamp}"
+    backup_dir.mkdir(parents=True, exist_ok=True)
 
-    if not VERSIONS_DIR.exists():
-        print("No existing migrations to backup")
+    total_backed_up = 0
+
+    for versions_dir in MODULE_MIGRATION_DIRS:
+        if not versions_dir.exists():
+            continue
+
+        migration_files = [f for f in versions_dir.glob("*.py") if f.name != "__init__.py"]
+        if not migration_files:
+            continue
+
+        # Create a subdirectory in backup matching the source path
+        rel_path = versions_dir.relative_to(project_root)
+        target_dir = backup_dir / str(rel_path).replace("/", "_")
+        target_dir.mkdir(parents=True, exist_ok=True)
+
+        for f in migration_files:
+            shutil.copy2(f, target_dir / f.name)
+            total_backed_up += 1
+
+        # Remove migration files from source (keep __init__.py)
+        for f in migration_files:
+            f.unlink()
+
+    if total_backed_up > 0:
+        print(f"Backed up {total_backed_up} migrations to {backup_dir.name}/")
+        return backup_dir
+    else:
+        print("No migration files found to backup")
+        backup_dir.rmdir()
         return None
 
-    migration_files = list(VERSIONS_DIR.glob("*.py"))
-    if not migration_files:
-        print("No migration files found")
-        return None
-
-    print(f"Backing up {len(migration_files)} migrations to {backup_dir.name}/")
-    shutil.copytree(VERSIONS_DIR, backup_dir)
-
-    # Clear versions directory (keep __pycache__ if exists)
-    for f in VERSIONS_DIR.glob("*.py"):
-        f.unlink()
-
-    return backup_dir
-
 
 def create_fresh_migration():
     """Generate fresh initial migration from models."""
@@ -116,7 +146,6 @@ def clean_migration_file(migration_path: Path):
     # Remove batch_alter_table references (not needed for PostgreSQL)
     if "batch_alter_table" in content:
         print("Note: Migration contains batch_alter_table - this is not needed for PostgreSQL")
-        # We don't auto-remove as it might be intentional
 
     print(f"Review migration at: {migration_path}")
 
@@ -178,14 +207,14 @@ def main():
         print(f"Backup location: {backup_dir}")
     print("")
     print("Next steps:")
-    print("1. Review the new migration file")
-    print("2. On a fresh database, run: make migrate-up")
+    print("1. Review the new migration files")
+    print("2. On a fresh database, run: make db-reset")
     print("3. Verify all tables are created correctly")
     print("4. If satisfied, delete the backup directory")
     print("")
-    print("To restore from backup:")
-    print(f"  rm -rf alembic/versions/*.py")
-    print(f"  cp -r {backup_dir}/* alembic/versions/")
+    if backup_dir:
+        print("To restore from backup:")
+        print(f"  Check {backup_dir}/ for backed up migration files")
 
 
 if __name__ == "__main__":