refactor(demo): Standardize demo account type names across codebase

Standardize demo account type naming from inconsistent variants to clean names:
- individual_bakery, professional_bakery → professional
- central_baker, enterprise_chain → enterprise

This eliminates naming confusion that was causing bugs in the demo session
initialization, particularly for enterprise demo tenants where different
parts of the system used different names for the same concept.

Changes:
- Updated source of truth in demo_session config
- Updated all backend services (middleware, cloning, orchestration)
- Updated frontend types, pages, and stores
- Updated demo session models and schemas
- Removed all backward compatibility code as requested

Related to: Enterprise demo session access fix

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/src/api/types/demo.ts

@@ -20,7 +20,7 @@
  * Backend: services/demo_session/app/api/schemas.py:10-15 (DemoSessionCreate)
  */
 export interface DemoSessionCreate {
-  demo_account_type: string;  // individual_bakery or central_baker
+  demo_account_type: string;  // professional or enterprise
   user_id?: string | null;  // Optional authenticated user ID
   ip_address?: string | null;
   user_agent?: string | null;