Remove the duplication of the ~18 per-hue dynamic tokens between
theme.css and buildThemeTokens(): theme.css now only defines fixed
neutrals, surfaces, layout and z-index; hue/mode-dependent values
come solely from tokens.ts, injected via SSR as an inline <style> in
+layout.svelte (tokensToCss helper) and reapplied on every hue
change. app.html sets data-theme before first paint by reading
localStorage, removing the dark flash when light mode was saved.
The two inline-style backgrounds become @utility
app-backdrop/app-vignette; the main's bottom padding becomes
@utility app-main, driven by --mf-dock-h via [data-has-track].
Note: <style>{expr}</style> doesn't interpolate in Svelte (it
compiles as component-scoped CSS) — the SSR block is injected with
{@html `<style>${css}</style>`} since the content is fully generated
(no user input).
Verified in the browser: --mf-accent/--mf-bg resolve correctly during
SSR, data-theme='light' applies before the first render with no
flash.
Updates the compose build context, the Dockerfile header, the package
name and the docs. The compose service and container keep the name
frontend/musify-frontend, since nginx routes to http://frontend:3000.
The source files also carry the first prettier pass, so the rename and
the reformat land together for them.