?brand=praktika re-skin: useBrand hook (reads ?brand= slug, fetches
/api/v1/brand/{slug}), runtime CSS-var override of accent palette +
Manrope font (open replacement for paid HalvarMittel), client logo in
Topbar, ?brand passthrough on the PDF link. No-op when ?brand= absent.
Migration 084 fills the praktika brand row (#235F49 / #1FCECB, logo, footer).
Closes#657