Add multiple features: auth, uploads, queue management, and filters

- Replace email with username for authentication
  - Update User model, schemas, and auth endpoints
  - Update frontend login and register views
  - Add migration to remove email column

- Add multiple track upload support
  - New backend endpoint for bulk upload
  - Frontend multi-file selection with progress
  - Auto-extract metadata from ID3 tags
  - Visual upload progress for each file

- Prevent duplicate tracks in room queue
  - Backend validation for duplicates
  - Visual indication of tracks already in queue
  - Error handling with user feedback

- Add bulk track selection for rooms
  - Multi-select mode with checkboxes
  - Bulk add endpoint with duplicate filtering
  - Selection counter and controls

- Add track filters in room modal
  - Search by title and artist
  - Filter by "My tracks"
  - Filter by "Not in queue"
  - Live filtering with result counter

- Improve Makefile
  - Add build-backend and build-frontend commands
  - Add rebuild-backend and rebuild-frontend commands
  - Add rebuild-clean variants
  - Update migrations to run in Docker

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

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

backend/alembic/versions/003_remove_email.py

@@ -0,0 +1,30 @@
+"""Remove email from users
+
+Revision ID: 003
+Revises: 002
+Create Date: 2024-12-19
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '003'
+down_revision: Union[str, None] = '002'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Drop unique constraint on email
+    op.drop_constraint('users_email_key', 'users', type_='unique')
+    # Drop email column
+    op.drop_column('users', 'email')
+
+
+def downgrade() -> None:
+    # Add email column back
+    op.add_column('users', sa.Column('email', sa.String(255), nullable=True))
+    # Add unique constraint back
+    op.create_unique_constraint('users_email_key', 'users', ['email'])