refactor(input): R10 S3b — one input recipe, ring focus everywhere

Unify text inputs onto the form.tsx inputCls look (surface bg, rounded-lg, 2px accent
RING focus), replacing the settings-family border-focus style app-wide:
- deleted 3 duplicate local `const inputCls` (KeyGate/SettingsPanel/SetupWizard) → import
  the shared one; a 4th (Welcome, py-2.5) kept local but re-styled to match.
- ~30 inline settings inputs: default full-size fields → inputCls; size variants (pager/
  table-filter/chat textarea/plex/glass-card) keep their width/radius/padding but swap
  bg-card→bg-surface and border-focus→ring-focus. glass-card/bg-transparent bgs left as-is.
- refreshed the form.tsx doc-comment (the old two-style split is gone).

The ring is the more visible / a11y-correct focus cue, matching R9's focus foundation.

frontend/src/components/Welcome.tsx

@@ -431,7 +431,7 @@ function AuthCard() {
   }
 
   const inputCls =
-    "w-full bg-card border border-border rounded-xl px-3 py-2.5 text-sm outline-hidden focus:border-accent";
+    "w-full bg-surface border border-border rounded-xl px-3 py-2.5 text-sm focus:outline-hidden focus:ring-2 focus:ring-accent/40";
   const titleKey = TITLE_KEY[mode];
 
   return (