feat: improve UI contrast, dark mode, dialog sizing, color coherence, and add table sorting

- Fix dialog scrollability (flex layout + max-h-[90dvh]) and increase L4 dialog to lg width
- Add styled enable card to L4 dialog matching proxy host pattern
- Unify section colors across proxy host and L4 dialogs (cyan=LB, emerald=DNS, violet=upstream DNS, rose=geo, amber=mTLS)
- Improve light mode contrast: muted-foreground oklch 0.552→0.502, remove opacity modifiers on secondary text
- Improve dark mode: boost muted-foreground to 0.85, increase border opacity 10%→16%, input 15%→20%
- Add bg-card to DataTable wrapper and bg-muted/40 to table headers for surface hierarchy
- Add semantic badge variants (success, warning, info, muted) and StatusChip dark mode fix
- Add server-side sortable columns to Proxy Hosts and L4 Proxy Hosts (name, upstream, status, protocol, listen)
- Add sortKey to DataTable Column type with clickable sort headers (ArrowUp/Down indicators, URL param driven)
- Fix E2E test selectors for shadcn UI (label associations, combobox roles, dropdown menus, mobile drawer)
- Add htmlFor/id to proxy host form fields and aria-labels to select triggers for accessibility
- Add sorting E2E tests for both proxy host pages

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/ui/AppDialog.tsx

@@ -46,7 +46,7 @@ export function AppDialog({
           <DialogTitle>{title}</DialogTitle>
         </DialogHeader>
 
-        <div className="overflow-y-auto py-4 px-1">{children}</div>
+        <div className="flex-1 min-h-0 overflow-y-auto py-4 px-1">{children}</div>
 
         <DialogFooter>
           {actions ?? (