Add theme-aware progress bar and image skeletons…

Details

Introduce a slim, reference-counted progress bar pinned to the top of
the viewport that tracks every Supabase request (config, news, sections,
links, documents and image blobs). It is wired in by wrapping the two
network primitives in db_assets (fetchWithTimeout and fetchAsObjectUrl),
so all DB-backed content is covered automatically.
DB images now show a shimmer skeleton in place of the browser's broken
image icon until their blob resolves. Colors are driven by the existing
CSS custom properties, so the bar and skeletons match both the v2
(accent orange) and v1 (accent blue) themes in light and dark mode, and
they respect prefers-reduced-motion.

Files changed (8)