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/app/openapi/importer.py

@@ -6,10 +6,11 @@ Each stage updates the job status and calls the on_progress callback.
 
 from __future__ import annotations
 
-import logging
 from collections.abc import Callable
 from dataclasses import replace
 
+import structlog
+
 from app.openapi.classifier import ClassifierProtocol, HeuristicClassifier
 from app.openapi.fetcher import fetch_spec
 from app.openapi.models import ImportJob
@@ -17,7 +18,7 @@ from app.openapi.parser import parse_endpoints
 from app.openapi.ssrf import DEFAULT_POLICY, SSRFPolicy
 from app.openapi.validator import validate_spec
 
-logger = logging.getLogger(__name__)
+logger = structlog.get_logger()
 
 ProgressCallback = Callable[[str, ImportJob], None] | None