style: rework overflow menu to look like menu items, not buttons

- Menu items now use text-xs font-light for smaller, lighter type
  that's clearly distinct from the pushbuttons in the action row
- The ··· button stays visually inverted (bg-fg text-bg) while the
  dropdown menu is open, reverting when closed
- Menu items styled as plain text rows with subtle hover background,
  no borders or button-like appearance

src/popup/index.html

@@ -319,7 +319,7 @@
                         >
                             <button
                                 id="btn-export-privkey"
-                                class="block w-full text-left px-4 py-1.5 text-sm hover:bg-hover cursor-pointer"
+                                class="block w-full text-left px-4 py-1.5 text-xs font-light text-muted hover:bg-hover hover:text-fg cursor-pointer"
                             >
                                 Export Private Key
                             </button>

src/popup/views/addressDetail.js

@@ -269,10 +269,13 @@ function init(_ctx) {
     const moreDropdown = $("more-menu-dropdown");
     moreBtn.addEventListener("click", (e) => {
         e.stopPropagation();
-        moreDropdown.classList.toggle("hidden");
+        const isOpen = !moreDropdown.classList.toggle("hidden");
+        moreBtn.classList.toggle("bg-fg", isOpen);
+        moreBtn.classList.toggle("text-bg", isOpen);
     });
     document.addEventListener("click", () => {
         moreDropdown.classList.add("hidden");
+        moreBtn.classList.remove("bg-fg", "text-bg");
     });
     moreDropdown.addEventListener("click", (e) => {
         e.stopPropagation();
@@ -280,6 +283,7 @@ function init(_ctx) {
 
     $("btn-export-privkey").addEventListener("click", () => {
         moreDropdown.classList.add("hidden");
+        moreBtn.classList.remove("bg-fg", "text-bg");
         const wallet = state.wallets[state.selectedWallet];
         const addr = wallet.addresses[state.selectedAddress];
         const title = addressTitle(addr.address, state.wallets);