UI polish noticed while testing Task 7101

Noticed on a local stack at 1366px and 390px while verifying Task 7101. 1. Project page at 390px: the "Add repository" button wraps onto two lines beside the Repositories heading. Keep it on one line (shorter label or full-width row on a phone). 2. An unknown path under `/settings/...` (now "Page not found") highlights Settings in the sidebar and the bottom nav. Highlight nothing for a not-found page. 3. Project page at 390px with every tab wrapped (Task 7101) takes three 44px rows. Consider a slightly tighter tab padding on phone so it fits in two. Out of scope: the not-found page itself and the Directory pane's action bar (Task 7101). Done means: - Each item fixed or explicitly rejected with a reason, checked visually at desktop and ≤480px width.

Fixed all 3 items (PR #5817, merged 98698fe): Add repository stays one line; not-found lights no nav row; phone tabs use 6px padding (2 rows at 390px). Quick gate green; visual check done at 390, 360 and 1366px. Deploy was superseded by later develop pushes. Follow-up draft #7166 filed.