feat: Improve file display, timezone handling, and LOT management

Changes:
- Fix datetime serialization with UTC 'Z' suffix for correct timezone display
- Add PDF upload support with extension fallback for MIME detection
- Fix LOT add/remove by creating new list for SQLAlchemy JSON change detection
- Add file message components (FileMessage, ImageLightbox, UploadPreview)
- Add multi-file upload support with progress tracking
- Link uploaded files to chat messages via message_id
- Include file attachments in AI report generation
- Update specs for file-storage, realtime-messaging, and ai-report-generation

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

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

app/modules/realtime/schemas.py

@@ -1,10 +1,17 @@
 """Pydantic schemas for WebSocket messages and REST API"""
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, ConfigDict, field_serializer
 from typing import Optional, Dict, Any, List
 from datetime import datetime
 from enum import Enum
 
 
+def serialize_datetime_utc(dt: datetime) -> str:
+    """Serialize datetime with 'Z' suffix to indicate UTC"""
+    if dt is None:
+        return None
+    return dt.isoformat() + "Z"
+
+
 class MessageTypeEnum(str, Enum):
     """Message type enumeration for validation"""
     TEXT = "text"
@@ -89,6 +96,13 @@ class MessageBroadcast(BaseModel):
     deleted_at: Optional[datetime] = None
     sequence_number: int
 
+    @field_serializer("created_at", "edited_at", "deleted_at")
+    def serialize_datetime(self, dt: Optional[datetime]) -> Optional[str]:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        if dt is None:
+            return None
+        return dt.isoformat() + "Z"
+
 
 class SystemMessageBroadcast(BaseModel):
     """System message broadcast"""
@@ -99,6 +113,11 @@ class SystemMessageBroadcast(BaseModel):
     timestamp: datetime
     data: Optional[Dict[str, Any]] = None
 
+    @field_serializer("timestamp")
+    def serialize_datetime(self, dt: datetime) -> str:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        return dt.isoformat() + "Z"
+
 
 class TypingBroadcast(BaseModel):
     """Typing indicator broadcast"""
@@ -115,6 +134,11 @@ class MessageAck(BaseModel):
     sequence_number: int
     timestamp: datetime
 
+    @field_serializer("timestamp")
+    def serialize_datetime(self, dt: datetime) -> str:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        return dt.isoformat() + "Z"
+
 
 class ErrorMessage(BaseModel):
     """Error message"""
@@ -145,16 +169,25 @@ class MessageResponse(BaseModel):
     sender_display_name: Optional[str] = None  # Display name from users table
     content: str
     message_type: MessageTypeEnum
-    metadata: Optional[Dict[str, Any]] = Field(None, alias="message_metadata")
+    # Use validation_alias to read from ORM's message_metadata, but serialize as "metadata"
+    metadata: Optional[Dict[str, Any]] = Field(None, validation_alias="message_metadata")
     created_at: datetime
     edited_at: Optional[datetime] = None
     deleted_at: Optional[datetime] = None
     sequence_number: int
     reaction_counts: Optional[Dict[str, int]] = None  # emoji -> count
 
-    class Config:
-        from_attributes = True
-        populate_by_name = True  # Allow both 'metadata' and 'message_metadata'
+    model_config = ConfigDict(
+        from_attributes=True,
+        populate_by_name=True,
+    )
+
+    @field_serializer("created_at", "edited_at", "deleted_at")
+    def serialize_datetime(self, dt: Optional[datetime]) -> Optional[str]:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        if dt is None:
+            return None
+        return dt.isoformat() + "Z"
 
 
 class MessageListResponse(BaseModel):
@@ -179,8 +212,12 @@ class ReactionResponse(BaseModel):
     emoji: str
     created_at: datetime
 
-    class Config:
-        from_attributes = True
+    model_config = ConfigDict(from_attributes=True)
+
+    @field_serializer("created_at")
+    def serialize_datetime(self, dt: datetime) -> str:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        return dt.isoformat() + "Z"
 
 
 class ReactionSummary(BaseModel):
@@ -195,12 +232,18 @@ class OnlineUser(BaseModel):
     user_id: str
     connected_at: datetime
 
+    @field_serializer("connected_at")
+    def serialize_datetime(self, dt: datetime) -> str:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        return dt.isoformat() + "Z"
+
 
 # File Upload WebSocket Schemas
 class FileUploadedBroadcast(BaseModel):
     """Broadcast when a file is uploaded to a room"""
     type: str = "file_uploaded"
     file_id: str
+    message_id: Optional[str] = None  # Associated chat message ID
     room_id: str
     uploader_id: str
     filename: str
@@ -208,6 +251,7 @@ class FileUploadedBroadcast(BaseModel):
     file_size: int
     mime_type: str
     download_url: Optional[str] = None
+    thumbnail_url: Optional[str] = None  # Thumbnail URL for images
     uploaded_at: datetime
 
     def to_dict(self) -> dict:
@@ -215,6 +259,7 @@ class FileUploadedBroadcast(BaseModel):
         return {
             "type": self.type,
             "file_id": self.file_id,
+            "message_id": self.message_id,
             "room_id": self.room_id,
             "uploader_id": self.uploader_id,
             "filename": self.filename,
@@ -222,7 +267,8 @@ class FileUploadedBroadcast(BaseModel):
             "file_size": self.file_size,
             "mime_type": self.mime_type,
             "download_url": self.download_url,
-            "uploaded_at": self.uploaded_at.isoformat()
+            "thumbnail_url": self.thumbnail_url,
+            "uploaded_at": self.uploaded_at.isoformat() + "Z"
         }
 
 
@@ -249,6 +295,7 @@ class FileDeletedBroadcast(BaseModel):
     """Broadcast when a file is deleted from a room"""
     type: str = "file_deleted"
     file_id: str
+    message_id: Optional[str] = None  # Associated chat message ID (also deleted)
     room_id: str
     deleted_by: str
     deleted_at: datetime
@@ -258,7 +305,27 @@ class FileDeletedBroadcast(BaseModel):
         return {
             "type": self.type,
             "file_id": self.file_id,
+            "message_id": self.message_id,
             "room_id": self.room_id,
             "deleted_by": self.deleted_by,
-            "deleted_at": self.deleted_at.isoformat()
+            "deleted_at": self.deleted_at.isoformat() + "Z"
+        }
+
+
+class MessageDeletedBroadcast(BaseModel):
+    """Broadcast when a message is deleted"""
+    type: str = "message_deleted"
+    message_id: str
+    room_id: str
+    deleted_by: str
+    deleted_at: datetime
+
+    def to_dict(self) -> dict:
+        """Convert to dictionary for WebSocket broadcast"""
+        return {
+            "type": self.type,
+            "message_id": self.message_id,
+            "room_id": self.room_id,
+            "deleted_by": self.deleted_by,
+            "deleted_at": self.deleted_at.isoformat() + "Z"
         }