fix: style private key as red well, remove explicit copy text

- Replace dashed border with light red well (bg-danger-well) and rounded corners
- Remove redundant 'Click to copy.' paragraph
- Add --color-danger-well theme token

src/popup/index.html

@@ -386,10 +386,9 @@
                 <div id="export-privkey-result" class="hidden">
                     <div
                         id="export-privkey-value"
-                        class="border border-dashed border-border p-2 font-mono text-xs break-all cursor-pointer mb-1"
+                        class="bg-danger-well rounded p-2 font-mono text-xs break-all cursor-pointer mb-1"
                         title="Click to copy"
                     ></div>
-                    <p class="text-xs text-muted">Click to copy.</p>
                 </div>
             </div>
 

src/popup/styles/main.css

@@ -11,6 +11,7 @@
     --color-border-light: #cccccc;
     --color-hover: #eeeeee;
     --color-well: #f5f5f5;
+    --color-danger-well: #fef2f2;
     --color-section: #dddddd;
 }