Polish desktop controls and navigation

[FreddyJD]

Summary

• add a subtle, anti-aliased single-stroke edge treatment across desktop controls, cards, menus, dialogs, and the composer
• align badges and danger controls with the shared squircle language while preserving semantic and non-worklet border fallbacks
• simplify the usage popover with an icon-free provider dropdown and compact cost counter
• keep Chat mounted behind secondary routes so returning from Settings is immediate and preserves transcript state
• translate idle and queued composer placeholders across all bundled locales

Implementation notes

• fixes the squircle ring cascade so hover, focus, accent, danger, and success colors can override the default
• paints the bevel and ring in one canvas stroke to avoid double-compositing anti-aliased corner pixels
• uses runtime edge/elevation tokens with light-theme overrides
• removes dead outer shadows from masked .sq controls

Verification

• npm run build
• npm run smoke:shared (1079 checks)
• npm run smoke:i18n (18 checks)
• Prettier
• git diff --check