Render top routes progressively

[cbusillo]

Summary

• reuse shared placeholder payloads so top-level workstation routes mount their shells immediately
• remove page-level RouteLoadingView gates from Folders, Ops, Completed, and Settings
• hydrate route data in onMount with inline pending/error states instead of blocking initial render
• keep Work using the same shared placeholders introduced by the previous first-load fix

Validation

• Browser reviewed /folders, /ops, /completed, and /settings at http://127.0.0.1:4173: no Loading workstation data; each mounts the real shell and hydrates data
• npm --prefix frontend run check
• npm --prefix frontend run test:unit -- --run
• bash scripts/pre-commit-check.sh