#18 Navbar+logo one bar (bullet separators, scrollable nav)

Context: Owner review round. Blocked by #15 (needs logo.svg). Tasks:

1. Single header bar: [logo] hu13 • <repo-name> + nav on one line (desktop); nav becomes horizontally scrollable strip (overflow-x:auto, no-wrap, scroll snap off, visible focus) on narrow. Separator • between brand cluster and nav, and between repo-name and nav? Spec: logo and navbar integrated into ONE bar separated by a •. Implement: brand-block logo + hu13 • nav-links • repo-name? Owner intent: logo+nav one unit, • separators. Keep: logo hu13 • code commits issues pulls tasks ci releases wiki • repo.
2. Active tab state (aria-current + accent underline) so position is visible.
3. Tests: header asserts (single <header>, • separators present, logo img alt, nav has scroll class, aria-current on active page). Success rubric:

• One header bar on all pages; scrollable nav verified in CSS (overflow-x:auto + nowrap); active state present. Swarm: Owl. Branch m6/navbar. Merge after #15.