fix tabs: use underline tab style with hover on all tabs

Tabs are not buttons (they change UI state, not application state).
All tabs now use underline style with identical hover behavior:
- Active: bold text + solid bottom border
- Inactive: muted text + transparent bottom border
- Hover (all tabs): text brightens to fg + bottom border appears
This ensures all tabs clearly indicate clickability on hover,
including the currently active one.

src/popup/views/addWallet.js

@@ -29,8 +29,12 @@ function switchMode(mode) {
         $("add-wallet-section-" + m).classList.toggle("hidden", m !== mode);
         const tab = $("tab-" + m);
         const isActive = m === mode;
-        tab.classList.toggle("bg-fg", isActive);
-        tab.classList.toggle("text-bg", isActive);
+        // Active: bold + solid underline
+        tab.classList.toggle("font-bold", isActive);
+        tab.classList.toggle("border-b-fg", isActive);
+        // Inactive: muted text + transparent underline
+        tab.classList.toggle("text-muted", !isActive);
+        tab.classList.toggle("border-b-transparent", !isActive);
     }
     $("add-wallet-password-hint").textContent = PASSWORD_HINTS[mode];
 }