feat(phase1): Complete development environment configuration

- Configure Alembic for database migrations with initial schema
- Fix base.py to use lazy loading for async engine (avoids import-time issues)
- Change AI model from sonnet to haiku (claude-3-haiku-20240307)
- Fix pytest version compatibility with pytest-asyncio
- Add frontend package-lock.json

Phase 1 tasks completed:
- F1.1: Development environment (Docker, Node.js 20, Python 3.12, venv)
- F1.2: PostgreSQL with 8 categories seeded
- F1.3: Redis connection verified
- F1.4: Anthropic API configured and tested
- F1.5: Backend server + WebSocket verified

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/alembic/script.py.mako

@@ -0,0 +1,26 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}