feat: RBAC Phase 1 — consolidate user roles into 4-value enum

Consolidate User.role (2-value: admin/store) + User.is_super_admin (boolean)
into a single 4-value UserRole enum: super_admin, platform_admin,
merchant_owner, store_member. Drop stale StoreUser.user_type column.
Fix role="user" bug in merchant creation.

Key changes:
- Expand UserRole enum from 2 to 4 values with computed properties
  (is_admin, is_super_admin, is_platform_admin, is_merchant_owner, is_store_user)
- Add Alembic migration (tenancy_003) for data migration + column drops
- Remove is_super_admin from JWT token payload
- Update all auth dependencies, services, routes, templates, JS, and tests
- Update all RBAC documentation

66 files changed, 1219 unit tests passing.

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

app/modules/messaging/models/message.py

@@ -42,8 +42,8 @@ class ConversationType(str, enum.Enum):
 class ParticipantType(str, enum.Enum):
     """Type of participant in a conversation."""
 
-    ADMIN = "admin"  # User with role="admin"
-    STORE = "store"  # User with role="store" (via StoreUser)
+    ADMIN = "admin"  # Platform admin user (super_admin or platform_admin)
+    STORE = "store"  # Store team user (merchant_owner or store_member)
     CUSTOMER = "customer"  # Customer model