refactor: migrate templates and static files to self-contained modules

Templates Migration:
- Migrate admin templates to modules (tenancy, billing, monitoring, marketplace, etc.)
- Migrate vendor templates to modules (tenancy, billing, orders, messaging, etc.)
- Migrate storefront templates to modules (catalog, customers, orders, cart, checkout, cms)
- Migrate public templates to modules (billing, marketplace, cms)
- Keep shared templates in app/templates/ (base.html, errors/, partials/, macros/)
- Migrate letzshop partials to marketplace module

Static Files Migration:
- Migrate admin JS to modules: tenancy (23 files), core (5 files), monitoring (1 file)
- Migrate vendor JS to modules: tenancy (4 files), core (2 files)
- Migrate shared JS: vendor-selector.js to core, media-picker.js to cms
- Migrate storefront JS: storefront-layout.js to core
- Keep framework JS in static/ (api-client, utils, money, icons, log-config, lib/)
- Update all template references to use module_static paths

Naming Consistency:
- Rename static/platform/ to static/public/
- Rename app/templates/platform/ to app/templates/public/
- Update all extends and static references

Documentation:
- Update module-system.md with shared templates documentation
- Update frontend-structure.md with new module JS organization

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

app/modules/messaging/exceptions.py

@@ -2,19 +2,13 @@
 """
 Messaging module exceptions.
 
-Re-exports messaging-related exceptions from their source locations.
+This module provides exception classes for messaging operations including:
+- Conversation management
+- Message handling
+- Attachment processing
 """
 
-from app.exceptions.message import (
-    ConversationNotFoundException,
-    MessageNotFoundException,
-    ConversationClosedException,
-    MessageAttachmentException,
-    UnauthorizedConversationAccessException,
-    InvalidConversationTypeException,
-    InvalidRecipientTypeException,
-    AttachmentNotFoundException,
-)
+from app.exceptions.base import BusinessLogicException, ResourceNotFoundException
 
 __all__ = [
     "ConversationNotFoundException",
@@ -26,3 +20,97 @@ __all__ = [
     "InvalidRecipientTypeException",
     "AttachmentNotFoundException",
 ]
+
+
+class ConversationNotFoundException(ResourceNotFoundException):
+    """Raised when a conversation is not found."""
+
+    def __init__(self, conversation_identifier: str):
+        super().__init__(
+            resource_type="Conversation",
+            identifier=conversation_identifier,
+            message=f"Conversation '{conversation_identifier}' not found",
+            error_code="CONVERSATION_NOT_FOUND",
+        )
+
+
+class MessageNotFoundException(ResourceNotFoundException):
+    """Raised when a message is not found."""
+
+    def __init__(self, message_identifier: str):
+        super().__init__(
+            resource_type="Message",
+            identifier=message_identifier,
+            message=f"Message '{message_identifier}' not found",
+            error_code="MESSAGE_NOT_FOUND",
+        )
+
+
+class ConversationClosedException(BusinessLogicException):
+    """Raised when trying to send message to a closed conversation."""
+
+    def __init__(self, conversation_id: int):
+        super().__init__(
+            message=f"Cannot send message to closed conversation {conversation_id}",
+            error_code="CONVERSATION_CLOSED",
+            details={"conversation_id": conversation_id},
+        )
+
+
+class MessageAttachmentException(BusinessLogicException):
+    """Raised when attachment validation fails."""
+
+    def __init__(self, message: str, details: dict | None = None):
+        super().__init__(
+            message=message,
+            error_code="MESSAGE_ATTACHMENT_INVALID",
+            details=details,
+        )
+
+
+class UnauthorizedConversationAccessException(BusinessLogicException):
+    """Raised when user tries to access a conversation they don't have access to."""
+
+    def __init__(self, conversation_id: int):
+        super().__init__(
+            message=f"You do not have access to conversation {conversation_id}",
+            error_code="CONVERSATION_ACCESS_DENIED",
+            details={"conversation_id": conversation_id},
+        )
+
+
+class InvalidConversationTypeException(BusinessLogicException):
+    """Raised when conversation type is not valid for the operation."""
+
+    def __init__(self, message: str, allowed_types: list[str] | None = None):
+        super().__init__(
+            message=message,
+            error_code="INVALID_CONVERSATION_TYPE",
+            details={"allowed_types": allowed_types} if allowed_types else None,
+        )
+
+
+class InvalidRecipientTypeException(BusinessLogicException):
+    """Raised when recipient type doesn't match conversation type."""
+
+    def __init__(self, conversation_type: str, expected_recipient_type: str):
+        super().__init__(
+            message=f"{conversation_type} conversations require a {expected_recipient_type} recipient",
+            error_code="INVALID_RECIPIENT_TYPE",
+            details={
+                "conversation_type": conversation_type,
+                "expected_recipient_type": expected_recipient_type,
+            },
+        )
+
+
+class AttachmentNotFoundException(ResourceNotFoundException):
+    """Raised when an attachment is not found."""
+
+    def __init__(self, attachment_id: int | str):
+        super().__init__(
+            resource_type="Attachment",
+            identifier=str(attachment_id),
+            message=f"Attachment '{attachment_id}' not found",
+            error_code="ATTACHMENT_NOT_FOUND",
+        )