fix(dashboard): render the snooze button, and cap the things-to-handle list (v0.23.15-beta)

Three faults in the same card, all layout.

**Snooze rendered as an unreadable sliver.** The row is a three-column grid —
severity bar, text, action — but carried four children once the snooze button
was added in v0.23.10. The fourth wrapped onto an implicit second row and landed
in column one, which is 3px wide, so the button was squeezed to nothing. The two
buttons now share the third column in a flex wrapper, which is what the grid
always assumed.

Only the rendering was broken: the dismiss round-trip was verified end to end
against the running instance — POST returns 201, the item leaves the list, the
snoozed count rises, and DELETE restores it.

**A long backlog pushed the rest of the dashboard off the page.** The list grew
without bound, so a fleet with real problems displaced everything below it. It
now caps at min(52vh, 460px) and scrolls, keeping the card a fixed part of the
page. The snoozed-count footer stays outside the scroll area so it remains
visible.

**The card rendered at 57% width with dead space beside it.** It was the only
child of a two-column grid left behind when quick actions moved to the header
(#104) — the comment above it already claimed full width, which it had not been
since. The empty column and its wrapper are gone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/version.ts

@@ -1 +1 @@
-export const APP_VERSION = 'v0.23.14 Beta';
+export const APP_VERSION = 'v0.23.15 Beta';