fix: polish mobile UI layouts

[zxh326]

What changed

• fixed the AI chat input on mobile so focusing the composer no longer hides the send button
• improved mobile behavior across shared UI primitives and high-traffic detail/list surfaces, including dialogs, popovers, selectors, monitoring filters, and dense toolbars
• updated resource detail headers so action buttons wrap on narrow screens instead of forcing horizontal scrolling
• narrowed responsive changes back toward desktop-first behavior so desktop tabs and standard layouts keep their original presentation

Why

Several UI surfaces were usable on desktop but broke down on phones, especially around fixed-width controls and action bars. The first visible bug was the AI chat composer, but the same pattern existed in other components.

User impact

• mobile users can use the AI chatbox, detail-page actions, and common selectors without horizontal scrolling or hidden controls
• desktop users keep the original tab styling and primary layout behavior

Root cause

A number of shared and page-level layouts assumed desktop widths and horizontal action groups. On small screens those assumptions caused controls to overflow or become inaccessible.

Validation

• ran pnpm build in ui/
• commit also passed the repository pre-commit formatting, vet, golangci-lint, and frontend eslint checks