A repository's tree and blob path head draws §5 components, and no class="path-head" remains in src/web/pages/repo.ts #4692

Done:

• [ ] Both path heads in src/web/pages/repo.ts (the tree's and the blob's: breadcrumb plus actions) draw with base.ts layout utilities and §5's bar for the actions; the breadcrumb keeps its links.
• [ ] A test fetches a tree page and a file page and asserts the breadcrumb links and no path-head.
• [ ] No layout shift: the breadcrumb and actions sit on one line on a wide screen and wrap under each other at 420px.

Markup only: the stylesheet and docs/DESIGN.md are not touched in this pull (their rules leave in a follow-up), so it cannot conflict with the many pulls editing src/web/style/content.ts. Replaces #4591, which reached its run cap with markup and rules in one pull. Run bun x tsc --noEmit, bun scripts/design-lint.ts and bun test test/design-lint.test.ts before pushing; where counts fall, lower docs/design/baseline.json in the same pull.