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>

alembic/versions/a1b2c3d4e5f6_add_message_id_to_room_files.py

@@ -0,0 +1,45 @@
+"""add message_id to room_files
+
+Revision ID: a1b2c3d4e5f6
+Revises: 4c5eb6e941db
+Create Date: 2025-12-08 12:00:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'a1b2c3d4e5f6'
+down_revision = '4c5eb6e941db'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Add message_id column to tr_room_files table
+    op.add_column('tr_room_files', sa.Column('message_id', sa.String(36), nullable=True))
+
+    # Add foreign key constraint
+    op.create_foreign_key(
+        'fk_room_files_message_id',
+        'tr_room_files',
+        'tr_messages',
+        ['message_id'],
+        ['message_id'],
+        ondelete='SET NULL'
+    )
+
+    # Add index for message_id
+    op.create_index('ix_tr_room_files_message', 'tr_room_files', ['message_id'])
+
+
+def downgrade() -> None:
+    # Remove index
+    op.drop_index('ix_tr_room_files_message', table_name='tr_room_files')
+
+    # Remove foreign key constraint
+    op.drop_constraint('fk_room_files_message_id', 'tr_room_files', type_='foreignkey')
+
+    # Remove column
+    op.drop_column('tr_room_files', 'message_id')