v0.5.3-beta: Database lifecycle & Alembic migration baseline

[DeepZone]

Motivation

• Provide a traceable, production-safe database lifecycle for RouteForge by introducing Alembic migration support and a documented upgrade process.
• Surface schema/migration state in the system status so operators can verify database migration health without exposing secrets.
• Keep local/demo SQLite behavior convenient while ensuring production/Postgres uses migrations rather than implicit schema creation.
• Ship migration-safe operational documentation and a clear baseline path for existing installations that used create_all.

Description

• Added an Alembic environment under backend/alembic including env.py, script.py.mako and the initial baseline migration 0001_initial_schema that creates api_cache, checks and reports.
• Extended backend system status logic (backend/app/core/system_status.py) to include schema_version, migration_status and migration_head, determined defensively via Alembic/SQLAlchemy with safe fallbacks.
• Changed startup behavior in backend/app/main.py to only call Base.metadata.create_all() for SQLite (dev/demo) and rely on Alembic for production/Postgres migrations.
• Updated frontend types and System UI (frontend/src/types.ts, frontend/src/App.tsx, frontend/src/components/Layout.tsx) to display schema version, migration head and a migration-status badge, and bumped visible versions to v0.5.3-beta.
• Added/updated docs (docs/operations/upgrades.md, docs/operations/backup-restore.md, docs/operations/database-migrations.md, README.md, RELEASE_NOTES.md) describing migration commands, baseline instructions (alembic stamp 0001_initial_schema) and a safe production workflow.
• Ensured container image can run Alembic by copying Alembic files into the backend image (backend/Dockerfile).

Testing

• Ran backend smoke tests with pytest backend/tests/test_api_smoke.py -q and all tests passed (15 passed).
• Built the frontend with npm run build and the production build completed successfully.
• Attempted docker compose -f docker-compose.prod.yml config but the Docker CLI is not available in this environment so that check was not executed here.

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Codex Task