feat(epub): enhance footnote styling and typography

- Add comprehensive footnote styling with Harvard Crimson theme colors
- Style footnote reference links with hover effects and proper superscript
- Improve footnote content typography with better spacing and readability
- Add visual separator line above footnotes section
- Style footnote numbers with crimson color and proper weight
- Enhance back-reference links with subtle hover effects
- Add special styling for code within footnotes
- Ensure footnotes are properly formatted and visually distinct

quarto/assets/styles/epub.css

@@ -516,6 +516,101 @@ figcaption {
     line-height: 1.4;
 }
 
+/* ==========================================================================
+   Footnotes and References
+   ========================================================================== */
+
+/* Footnote reference links (superscript numbers in text) */
+a[href^="#fn-"],
+.footnote-ref {
+    font-size: 0.75em;
+    vertical-align: super;
+    text-decoration: none;
+    color: var(--crimson);
+    font-weight: 600;
+    padding: 0 2px;
+    border-radius: 2px;
+    transition: background-color 0.2s ease;
+}
+
+a[href^="#fn-"]:hover,
+.footnote-ref:hover {
+    background-color: rgba(165, 28, 48, 0.1);
+    text-decoration: none;
+}
+
+/* Footnote content styling */
+.footnotes,
+div[id^="fn-"],
+.footnote {
+    margin-top: 2rem;
+    padding-top: 1rem;
+    border-top: 2px solid var(--border-light);
+    font-size: 0.85rem;
+    line-height: 1.5;
+    color: var(--text-secondary);
+}
+
+/* Individual footnote entries */
+.footnotes ol,
+.footnotes ul {
+    padding-left: 1.5rem;
+    margin: 0;
+}
+
+.footnotes li {
+    margin-bottom: 0.75rem;
+    padding-left: 0.25rem;
+}
+
+/* Footnote numbers */
+.footnotes li::marker {
+    color: var(--crimson);
+    font-weight: 600;
+}
+
+/* Back-reference links in footnotes */
+a[href^="#fnref-"],
+.footnote-back {
+    font-size: 0.8em;
+    color: var(--text-muted);
+    text-decoration: none;
+    margin-left: 0.5rem;
+    padding: 2px 4px;
+    border-radius: 2px;
+    transition: all 0.2s ease;
+}
+
+a[href^="#fnref-"]:hover,
+.footnote-back:hover {
+    color: var(--crimson);
+    background-color: rgba(165, 28, 48, 0.05);
+    text-decoration: none;
+}
+
+/* Footnote separator styling */
+.footnotes::before {
+    content: "";
+    display: block;
+    width: 60px;
+    height: 1px;
+    background-color: var(--crimson);
+    margin: 0 0 1rem 0;
+}
+
+/* Enhanced footnote typography */
+.footnotes p {
+    margin-bottom: 0.5rem;
+    text-align: left;
+}
+
+.footnotes code {
+    font-size: 0.8em;
+    background-color: rgba(165, 28, 48, 0.05);
+    padding: 1px 3px;
+    border-radius: 2px;
+}
+
 /* ==========================================================================
    Lists and Navigation
    ========================================================================== */