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/file_storage/schemas.py

@@ -1,5 +1,5 @@
 """Pydantic schemas for file storage operations"""
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field, field_validator, field_serializer, ConfigDict
 from typing import Optional, List
 from datetime import datetime
 from enum import Enum
@@ -15,21 +15,28 @@ class FileType(str, Enum):
 class FileUploadResponse(BaseModel):
     """Response after successful file upload"""
     file_id: str
+    message_id: Optional[str] = None  # Associated chat message ID
     filename: str
     file_type: FileType
     file_size: int
     mime_type: str
     download_url: str  # Presigned URL
+    thumbnail_url: Optional[str] = None  # Thumbnail URL for images
     uploaded_at: datetime
     uploader_id: str
 
-    class Config:
-        from_attributes = True
+    model_config = ConfigDict(from_attributes=True)
+
+    @field_serializer("uploaded_at")
+    def serialize_datetime(self, dt: datetime) -> str:
+        """Serialize datetime with 'Z' suffix to indicate UTC"""
+        return dt.isoformat() + "Z"
 
 
 class FileMetadata(BaseModel):
     """File metadata response"""
     file_id: str
+    message_id: Optional[str] = None  # Associated chat message ID
     room_id: str
     filename: str
     file_type: FileType
@@ -41,9 +48,9 @@ class FileMetadata(BaseModel):
     uploader_id: str
     deleted_at: Optional[datetime] = None
     download_url: Optional[str] = None  # Presigned URL (only when requested)
+    thumbnail_url: Optional[str] = None  # Thumbnail URL for images
 
-    class Config:
-        from_attributes = True
+    model_config = ConfigDict(from_attributes=True)
 
     @field_validator("file_size")
     @classmethod
@@ -53,6 +60,13 @@ class FileMetadata(BaseModel):
             raise ValueError("File size must be positive")
         return v
 
+    @field_serializer("uploaded_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 FileListResponse(BaseModel):
     """Paginated file list response"""
@@ -62,13 +76,11 @@ class FileListResponse(BaseModel):
     offset: int
     has_more: bool
 
-    class Config:
-        from_attributes = True
+    model_config = ConfigDict(from_attributes=True)
 
 
 class FileUploadParams(BaseModel):
     """Parameters for file upload (optional description)"""
     description: Optional[str] = Field(None, max_length=500)
 
-    class Config:
-        from_attributes = True
+    model_config = ConfigDict(from_attributes=True)