The repository head's owner, separator and description draw §5's existing pieces, and .owner, .slash and .repo-desc leave the stylesheet #4808

Intent: the repository head uses classes §5 already has, so the design check has nothing new to count. Replaces #4593. Both of its pulls (#4650, #4682) went red on "design check … the tree is no worse than its baseline" because they invented a new head component.

Done:

• [ ] in src/web/chrome.ts (about lines 310–330), the owner (class="owner") draws as base.ts's .muted link or span, and the separator (class="slash") as the .sep that src/web/style/components.ts already defines
• [ ] the description (<p class="repo-desc">) draws as base.ts's .muted .small, keeping its 4 px gap under the title through the head's existing layout
• [ ] .repo-title .owner, .repo-title .slash and .repo-desc leave src/web/style/content.ts, and .owner, .slash and .repo-desc leave docs/DESIGN.md §5d. .repo-title stays, as the head's title style
• [ ] no new class, no inline style and no new docs/design/areas file; bun scripts/design-lint.ts prints nothing new, and docs/design/baseline.json is never raised
• [ ] a test fetches a repository page and asserts the head's owner link, .sep and description, and no class="owner", class="slash" or repo-desc

Files: src/web/chrome.ts, src/web/style/content.ts, docs/DESIGN.md and one test. Run bun scripts/design-lint.ts and bun test test/design-lint.test.ts before pushing.