feat(docs): add footer, favicon, and GitHub link

- Add sidebar footer with GitHub repo link and MIT copyright
- Position footer at bottom of sidebar using flexbox
- Generate geometric logo and add as favicon
- Update base.html template with footer and favicon link

docs/static/style.css

@@ -41,6 +41,8 @@ body {
   top: 0;
   height: 100vh;
   overflow-y: auto;
+  display: flex;
+  flex-direction: column;
 }
 
 .sidebar header {
@@ -85,6 +87,25 @@ body {
   color: var(--bg);
 }
 
+.sidebar-footer {
+  margin-top: auto;
+  padding-top: 1rem;
+  border-top: 1px solid var(--border);
+  font-size: 0.75rem;
+  color: var(--fg-muted);
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+}
+
+.sidebar-footer a {
+  color: var(--fg-muted);
+}
+
+.sidebar-footer a:hover {
+  color: var(--accent);
+}
+
 /* Main content */
 main {
   padding: 3rem 4rem;