Add operator dashboard

[Bmowville]

Summary

• add a read-only /dashboard page backed by the operations overview endpoint
• redirect / to the dashboard for a clearer first-run experience
• include dashboard assets in packaged builds
• document the product direction and demo dashboard flow
• add route and static asset tests

Validation

• python -m ruff check .
• python -m mypy app
• python -m alembic upgrade head
• python -m pytest
• git diff --check
• browser-checked /dashboard with seeded sample data