fix(css): keep full-width modal fields inside their clipped container

Two stacked defects cut the side edges off the URL textareas in the
download and batch-import modals.

`#modelUrl` and `#batchUrlInput` are `width: 100%` with padding and a
border but no `box-sizing: border-box`, so the border box was wider than
the containing block and its right edge landed in the region the modal
clips: the right border column is missing in both screenshots while the
corner pixels of the top/bottom borders are drawn, and the batch
textarea's resize handle sits a padding-width to the right of the mode
toggle above it.

The download modal's `#downloadModal .download-step` additionally
scrolls with `overflow-x: hidden` and has no horizontal padding, so the
global `:focus-visible { outline-offset: 2px }` lost both vertical edges
there and only the top and bottom lines survived. Draw that ring inset
inside `#downloadModal`, mirroring the existing `#importModal` fix in
import-modal.css.

`.input-group input, .input-group select` gets the same border-box
treatment, which also repairs the standing clipped right border on the
other full-width fields the shared rule styles (the import modal's URL,
recipe-name and tag inputs, the batch directory and tags inputs, the
model root select and the target folder path).

Verified: `npx vitest run` 130 files / 1259 tests passed.

static/css/components/batch-import-modal.css

@@ -31,6 +31,10 @@
 /* Textarea Styling */
 #batchUrlInput {
     width: 100%;
+    /* Content-box sizing made the border box wider than the modal's content
+       box, so the right border/halo fell outside the clipped area and was cut
+       off. Include padding and border in the declared width. */
+    box-sizing: border-box;
     min-height: 120px;
     padding: 12px;
     border: 1px solid var(--border-color);