refactor: centralize frontend detection with FrontendDetector

Major architecture change to unify frontend detection:

## Problem Solved
- Eliminated code duplication across 3 middleware files
- Fixed incomplete path detection (now detects /api/v1/admin/*)
- Unified on FrontendType enum (deprecates RequestContext)
- Added request.state.frontend_type for all requests

## New Components
- app/core/frontend_detector.py: Centralized FrontendDetector class
- middleware/frontend_type.py: FrontendTypeMiddleware (replaces ContextMiddleware)
- docs/architecture/frontend-detection.md: Complete architecture documentation

## Changes
- main.py: Use FrontendTypeMiddleware instead of ContextMiddleware
- middleware/context.py: Deprecated (kept for backwards compatibility)
- middleware/platform_context.py: Use FrontendDetector.is_admin()
- middleware/vendor_context.py: Use FrontendDetector.is_admin()
- middleware/language.py: Use FrontendType instead of context_value
- app/exceptions/handler.py: Use FrontendType.STOREFRONT
- app/exceptions/error_renderer.py: Use FrontendType
- Customer routes: Cookie path changed from /shop to /storefront

## Documentation
- docs/architecture/frontend-detection.md: New comprehensive docs
- docs/architecture/middleware.md: Updated for new system
- docs/architecture/request-flow.md: Updated for FrontendType
- docs/backend/middleware-reference.md: Updated API reference

## Tests
- tests/unit/core/test_frontend_detector.py: 37 new tests
- tests/unit/middleware/test_frontend_type.py: 11 new tests
- tests/unit/middleware/test_context.py: Updated for compatibility

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

app/exceptions/handler.py

@@ -16,7 +16,8 @@ from fastapi import HTTPException, Request
 from fastapi.exceptions import RequestValidationError
 from fastapi.responses import JSONResponse, RedirectResponse
 
-from middleware.context import RequestContext, get_request_context
+from app.modules.enums import FrontendType
+from middleware.frontend_type import get_frontend_type
 
 from .base import WizamartException
 from .error_renderer import ErrorPageRenderer
@@ -382,17 +383,17 @@ def _is_html_page_request(request: Request) -> bool:
 
 def _redirect_to_login(request: Request) -> RedirectResponse:
     """
-    Redirect to appropriate login page based on request context.
+    Redirect to appropriate login page based on request frontend type.
 
-    Uses context detection to determine admin vs vendor vs shop login.
+    Uses FrontendType detection to determine admin vs vendor vs storefront login.
     Properly handles multi-access routing (domain, subdomain, path-based).
     """
-    context_type = get_request_context(request)
+    frontend_type = get_frontend_type(request)
 
-    if context_type == RequestContext.ADMIN:
+    if frontend_type == FrontendType.ADMIN:
         logger.debug("Redirecting to /admin/login")
         return RedirectResponse(url="/admin/login", status_code=302)
-    if context_type == RequestContext.VENDOR_DASHBOARD:
+    if frontend_type == FrontendType.VENDOR:
         # Extract vendor code from the request path
         # Path format: /vendor/{vendor_code}/...
         path_parts = request.url.path.split("/")
@@ -417,8 +418,8 @@ def _redirect_to_login(request: Request) -> RedirectResponse:
 
         logger.debug(f"Redirecting to {login_url}")
         return RedirectResponse(url=login_url, status_code=302)
-    if context_type == RequestContext.SHOP:
-        # For shop context, redirect to shop login (customer login)
+    if frontend_type == FrontendType.STOREFRONT:
+        # For storefront context, redirect to storefront login (customer login)
         # Calculate base_url for proper routing (supports domain, subdomain, and path-based access)
         vendor = getattr(request.state, "vendor", None)
         vendor_context = getattr(request.state, "vendor_context", None)
@@ -437,11 +438,11 @@ def _redirect_to_login(request: Request) -> RedirectResponse:
             )
             base_url = f"{full_prefix}{vendor.subdomain}/"
 
-        login_url = f"{base_url}shop/account/login"
+        login_url = f"{base_url}storefront/account/login"
         logger.debug(f"Redirecting to {login_url}")
         return RedirectResponse(url=login_url, status_code=302)
-    # Fallback to root for unknown contexts
-    logger.debug("Unknown context, redirecting to /")
+    # Fallback to root for unknown contexts (PLATFORM)
+    logger.debug("Platform context, redirecting to /")
     return RedirectResponse(url="/", status_code=302)