refactor: migrate vendor APIs to token-based context and consolidate architecture

## Vendor-in-Token Architecture (Complete Migration)
- Migrate all vendor API endpoints from require_vendor_context() to token_vendor_id
- Update permission dependencies to extract vendor from JWT token
- Add vendor exceptions: VendorAccessDeniedException, VendorOwnerOnlyException,
  InsufficientVendorPermissionsException
- Shop endpoints retain require_vendor_context() for URL-based detection
- Add AUTH-004 architecture rule enforcing vendor context patterns
- Fix marketplace router missing /marketplace prefix

## Exception Pattern Fixes (API-003/API-004)
- Services raise domain exceptions, endpoints let them bubble up
- Add code_quality and content_page exception modules
- Move business logic from endpoints to services (admin, auth, content_page)
- Fix exception handling in admin, shop, and vendor endpoints

## Tailwind CSS Consolidation
- Consolidate CSS to per-area files (admin, vendor, shop, platform)
- Remove shared/cdn-fallback.html and shared/css/tailwind.min.css
- Update all templates to use area-specific Tailwind output files
- Remove Node.js config (package.json, postcss.config.js, tailwind.config.js)

## Documentation & Cleanup
- Update vendor-in-token-architecture.md with completed migration status
- Update architecture-rules.md with new rules
- Move migration docs to docs/development/migration/
- Remove duplicate/obsolete documentation files
- Merge pytest.ini settings into pyproject.toml

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

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

app/exceptions/admin.py

@@ -236,3 +236,37 @@ class VendorVerificationException(BusinessLogicException):
             error_code="VENDOR_VERIFICATION_FAILED",
             details=details,
         )
+
+
+class UserCannotBeDeletedException(BusinessLogicException):
+    """Raised when a user cannot be deleted due to ownership constraints."""
+
+    def __init__(self, user_id: int, reason: str, owned_count: int = 0):
+        details = {
+            "user_id": user_id,
+            "reason": reason,
+        }
+        if owned_count > 0:
+            details["owned_companies_count"] = owned_count
+
+        super().__init__(
+            message=f"Cannot delete user {user_id}: {reason}",
+            error_code="USER_CANNOT_BE_DELETED",
+            details=details,
+        )
+
+
+class UserRoleChangeException(BusinessLogicException):
+    """Raised when user role cannot be changed."""
+
+    def __init__(self, user_id: int, current_role: str, target_role: str, reason: str):
+        super().__init__(
+            message=f"Cannot change user {user_id} role from {current_role} to {target_role}: {reason}",
+            error_code="USER_ROLE_CHANGE_FAILED",
+            details={
+                "user_id": user_id,
+                "current_role": current_role,
+                "target_role": target_role,
+                "reason": reason,
+            },
+        )