#3601 [GUI] fix Model settings fields overflowing their card at 1280x720

Description

## Problem

At 1280x720, About -> Model settings overflows its card. The form's label column is sized `minmax(180px, max-content)`, so the longest config key/help text widens it without bound; the right column is then squeezed, and the inputs and selects are clipped by the card edge. The same page is fine at larger sizes where the content is narrower relative to the window.

## Fix

In `serve/web/app.css` only:

- `grid-template-columns: 75% minmax(0, 1fr)`: a stable label column and the rest for the field, which can shrink (`minmax(0, ...)`).
- `overflow-wrap: anywhere` on the label, so a long key wraps instead of widening the column.
- `width: 100%; min-width: 0` on `.cfg-form .st-input`, so the field fills its column and never overflows.

No DOM, JavaScript or endpoint changes. The existing `@media (max-width: 1000px)` single-column rule is untouched.

## Validation

Served the page from a local 0.1.47 server and checked About -> Model settings at 1280x720: labels wrap, fields stay inside the card, and the Save row is unchanged. Not tested at other window sizes or in other browsers.