feat: add copy-flash visual feedback on click-to-copy

When a user clicks to copy text (addresses, tx hashes, etc.), the copied
element now briefly flashes with inverted colors (bg/fg swap) and fades
back over ~300ms. This provides localized visual feedback in addition to
the existing flash message.

Applied to all click-to-copy elements across all views.

closes #100

src/popup/views/home.js

@@ -2,6 +2,7 @@ const {
     $,
     showView,
     showFlash,
+    flashCopyFeedback,
     balanceLinesForAddress,
     isoDate,
     timeAgo,
@@ -85,9 +86,10 @@ function renderActiveAddress() {
         el.innerHTML =
             `<span class="underline decoration-dashed cursor-pointer" id="active-addr-copy">${dot}${escapeHtml(addr)}</span>` +
             `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
-        $("active-addr-copy").addEventListener("click", () => {
+        $("active-addr-copy").addEventListener("click", (e) => {
             navigator.clipboard.writeText(addr);
             showFlash("Copied!");
+            flashCopyFeedback(e.currentTarget);
         });
     } else {
         el.textContent = "";