docs: update authentication dependency names across documentation

Updated all documentation to use correct authentication dependency names:
- HTML pages: get_current_admin_from_cookie_or_header, get_current_vendor_from_cookie_or_header, get_current_customer_from_cookie_or_header
- API endpoints: get_current_admin_api, get_current_vendor_api, get_current_customer_api

Changes:
- Updated authentication flow diagrams with correct dependency names for admin and vendor flows
- Added comprehensive customer/shop authentication flow documentation
- Updated cookie isolation architecture to show all three contexts (admin, vendor, shop)
- Expanded security boundary enforcement diagram to include shop routes
- Added customer cross-context prevention examples
- Updated all code examples in frontend and backend documentation
- Fixed import statements to use app.api.deps instead of app.core.auth

Files updated:
- docs/api/authentication-flow-diagrams.md (added customer flows)
- docs/frontend/admin/page-templates.md
- docs/frontend/admin/architecture.md
- docs/frontend/shared/ui-components.md
- docs/frontend/shared/sidebar.md
- docs/development/exception-handling.md
- docs/architecture/diagrams/vendor-domain-diagrams.md
- docs/backend/admin-integration-guide.md
- docs/backend/admin-feature-integration.md

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

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

docs/backend/admin-feature-integration.md

@@ -943,7 +943,7 @@ from typing import List
 from fastapi import APIRouter, Depends, Path, Body, Query
 from sqlalchemy.orm import Session
 
-from app.api.deps import get_current_admin_user, get_db
+from app.api.deps import get_current_admin_api, get_db
 from app.services.vendor_domain_service import vendor_domain_service
 from app.exceptions import VendorNotFoundException
 from models.schema.vendor_domain import (
@@ -992,7 +992,7 @@ def add_vendor_domain(
     vendor_id: int = Path(..., description="Vendor ID", gt=0),
     domain_data: VendorDomainCreate = Body(...),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_user),
+    current_admin: User = Depends(get_current_admin_api),
 ):
     """
     Add a custom domain to vendor (Admin only).
@@ -1040,7 +1040,7 @@ def add_vendor_domain(
 def list_vendor_domains(
     vendor_id: int = Path(..., description="Vendor ID", gt=0),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_user),
+    current_admin: User = Depends(get_current_admin_api),
 ):
     """
     List all domains for a vendor (Admin only).
@@ -1084,7 +1084,7 @@ def update_vendor_domain(
     domain_id: int = Path(..., description="Domain ID", gt=0),
     domain_update: VendorDomainUpdate = Body(...),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_user),
+    current_admin: User = Depends(get_current_admin_api),
 ):
     """
     Update domain settings (Admin only).
@@ -1127,7 +1127,7 @@ def update_vendor_domain(
 def delete_vendor_domain(
     domain_id: int = Path(..., description="Domain ID", gt=0),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_user),
+    current_admin: User = Depends(get_current_admin_api),
 ):
     """
     Delete a custom domain (Admin only).
@@ -1193,7 +1193,7 @@ router.include_router(users.router, tags=["admin-users"])
 async def admin_vendor_domains_page(
         request: Request,
         vendor_code: str = Path(..., description="Vendor code"),
-        current_user: User = Depends(get_current_admin_user),
+        current_user: User = Depends(get_current_admin_from_cookie_or_header),
         db: Session = Depends(get_db)
 ):
     """