The new issue and new pull forms speak the home page's language #9719

For: someone starting work or contributing to a repository begins at these two forms. They are the next page in the design pass, and P1 Feed has nothing ready.

Done looks like:

• [x] The compose forms in src/web/pages/issues.ts and src/web/pages/pulls.ts follow the opening principles of docs/DESIGN.md: one column, space instead of boxes, labels in the home page's type, one primary action.
• [x] Nothing is lost: the prefill from C (#8885), labels, sealed reports, the cross-repository base/head choice, guest refusals and the title and body limits all work as before, with JavaScript off too.
• [x] The forms fit a 390 px phone with no sideways scroll. test/issues-fit.test.ts and test/pulls-fit.test.ts cover the compose forms, and those tests fail if the forms scroll sideways.
• [x] bun scripts/design-lint.ts passes, and so do test/issues*.test.ts and test/pulls*.test.ts.

Files: src/web/pages/issues.ts, src/web/pages/pulls.ts, and their area docs under docs/design/areas/ if a class is added. Risks: the words come from actions/*_words.ts and core/contribute.ts. Reuse them and do not copy them, or tests that pin them will fail.

Reviewed pull #9724 at its head: ticked The compose forms in src/web/pages/issues.ts and src/web/pages/pulls.ts follow the opening principles of docs/DESIGN.md: one column, space instead of boxes, labels in the home page's type, one primary action.; Nothing is lost: the prefill from C (#8885), labels, sealed reports, the cross-repository base/head choice, guest refusals and the title and body limits all work as before, with JavaScript off too.; The forms fit a 390 px phone with no sideways scroll. test/issues-fit.test.ts and test/pulls-fit.test.ts cover the compose forms, and those tests fail if the forms scroll sideways.; bun scripts/design-lint.ts passes, and so do test/issues*.test.ts and test/pulls*.test.ts..