fix(mobile): stop the native date input from overflowing the issue page

[exe-dev-github-integration]

Problem

On the issue view on a phone, the page scrolls sideways and every field (Status, Priority, Estimate, Due date) plus the title and header run off the right edge — reported with a screenshot showing all the field boxes shifted past the screen.

Cause

The issue page's field strip is an <aside> grid item (from the #45 layout). Grid items default to min-width: auto, so they won't shrink below their content's intrinsic width. A native filled <input type="date"> has a wide intrinsic width on iOS, so it became the aside's minimum and stretched the aside — and every w-full field inside it — past the viewport, forcing document-level horizontal scroll.

The earlier mobile audit + CI missed it because (a) the test issue had no due date and (b) Chromium renders date inputs compactly (~110px) where iOS renders them much wider.

Fix

• Issue page: min-w-0 on the field <aside> (lets the grid track constrain it) and on the date input (pins the native control to the column width via its existing w-full).
• Global phone hardening (styles.css, ≤639px): every input/select/textarea gets min-width: 0; max-width: 100%, so no native control can push past its container — this also covers the new-issue dialog's date field, which sits in a flex row with the identical risk.

Verification

• tsc -b clean; bun run test → 84 pass.
• Mobile viewport (390, with a due date set): issue page and new-issue dialog both report 0px horizontal page overflow; the date input is constrained to its column (361px) rather than dictating width. Desktop (1440) layout unchanged (fields stay the 14rem right column, no overflow).
• ⚠️ The iOS-specific intrinsic date width isn't reproducible in headless Chromium, so the structural min-width:0 fix wants an on-device confirm — but the mechanism (grid item min-width:auto → native-control overflow) is well understood and the standard fix.