The page head is a §5 component: `.page-head` moves from §5d into the table, with the function that draws it #4832

Intent: the head on most pages (title, subtitle, actions) is a component the table names, because that is what it is. This is the §5d path "into the table when a page-local thing turns out to be a component".

Done:

• [ ] the .page-head rules move unchanged from src/web/style/content.ts to src/web/style/components.ts
• [ ] docs/DESIGN.md §5's table gains a page head row naming the function in src/web/chrome.ts that draws it, the class and its parts. .page-head leaves the §5d content.ts list
• [ ] pages that write class="page-head" by hand instead of calling that function are listed in the pull, and none is changed in it
• [ ] the served stylesheet is byte-for-byte the same apart from the move; a test asserts .page-head is defined once

Files: src/web/style/content.ts, src/web/style/components.ts, docs/DESIGN.md and one test. If #4749 (.sub) has landed, move what is left of it.

Run bun scripts/design-lint.ts and bun test test/design-lint.test.ts before pushing; lower docs/design/baseline.json only where a count fell, never raise it. Keep the diff to the files named.