Polish share buttons to match Tufte aesthetic

Remove bright colored backgrounds from share buttons:
- Removed Twitter blue (#1DA1F2) from Tweet button
- Removed Facebook blue (#4267B2) from Share button
- Simplified "copied" state to subtle border/text color change

All buttons now use elegant default styling with subtle borders
and proper hover states. Icons (📋, 🐦, f) provide visual differentiation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

kjvstudy_org/templates/verse.html

@@ -95,32 +95,9 @@
     color: var(--link-color);
 }
 
-.share-btn.twitter {
-    background: #1DA1F2;
-    color: white;
-    border-color: #1DA1F2;
-}
-
-.share-btn.twitter:hover {
-    background: #0d8bd9;
-    border-color: #0d8bd9;
-}
-
-.share-btn.facebook {
-    background: #4267B2;
-    color: white;
-    border-color: #4267B2;
-}
-
-.share-btn.facebook:hover {
-    background: #365899;
-    border-color: #365899;
-}
-
 .share-btn.copied {
-    background: #28a745;
-    color: white;
-    border-color: #28a745;
+    border-color: var(--link-color);
+    color: var(--link-color);
 }
 
 /* Cross-reference tooltip styles */