refactor: engineering improvements -- API versioning, structured logging, Alembic, error standardization, test coverage

- API versioning: all REST endpoints prefixed with /api/v1/
- Structured logging: replaced stdlib logging with structlog (console/JSON modes)
- Alembic migrations: versioned DB schema with initial migration
- Error standardization: global exception handlers for consistent envelope format
- Interrupt cleanup: asyncio background task for expired interrupt removal
- Integration tests: +30 tests (analytics, replay, openapi, error, session APIs)
- Frontend tests: +57 tests (all components, pages, useWebSocket hook)
- Backend: 557 tests, 89.75% coverage | Frontend: 80 tests, 16 test files

backend/alembic/env.py

@@ -0,0 +1,67 @@
+"""Alembic environment configuration for smart-support."""
+
+from __future__ import annotations
+
+import os
+from logging.config import fileConfig
+
+from sqlalchemy import engine_from_config, pool
+
+from alembic import context
+
+config = context.config
+
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# No SQLAlchemy ORM models -- we use raw DDL migrations
+target_metadata = None
+
+
+def _get_url() -> str:
+    """Read DATABASE_URL from environment, falling back to alembic.ini."""
+    return os.environ.get("DATABASE_URL", "") or config.get_main_option(
+        "sqlalchemy.url", ""
+    )
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    Configures the context with just a URL so that an Engine
+    is not required.
+    """
+    url = _get_url()
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode with a live database connection."""
+    configuration = config.get_section(config.config_ini_section, {})
+    configuration["sqlalchemy.url"] = _get_url()
+
+    connectable = engine_from_config(
+        configuration,
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(connection=connection, target_metadata=target_metadata)
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()