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/models.py

@@ -16,6 +16,9 @@ class RoomFile(Base):
     # Foreign key to incident room (CASCADE delete when room is permanently deleted)
     room_id = Column(String(36), ForeignKey("tr_incident_rooms.room_id", ondelete="CASCADE"), nullable=False)
 
+    # Foreign key to associated message (nullable for legacy files)
+    message_id = Column(String(36), ForeignKey("tr_messages.message_id", ondelete="SET NULL"), nullable=True)
+
     # File metadata
     uploader_id = Column(String(255), nullable=False)
     filename = Column(String(255), nullable=False)
@@ -33,11 +36,13 @@ class RoomFile(Base):
 
     # Relationships
     room = relationship("IncidentRoom", back_populates="files")
+    message = relationship("Message", backref="file_attachment", uselist=False)
 
     # Indexes
     __table_args__ = (
         Index("ix_tr_room_files_room_uploaded", "room_id", "uploaded_at"),
         Index("ix_tr_room_files_uploader", "uploader_id"),
+        Index("ix_tr_room_files_message", "message_id"),
     )
 
     def __repr__(self):