appview/pages/markup: add footnot support

Signed-off-by: oppiliappan <[e-mail]>

appview/pages/markup/markdown.go

···
 				),
 				highlighting.WithCustomStyle(styles.Get("catppuccin-latte")),
 			),
+			extension.NewFootnote(
+				extension.WithFootnoteIDPrefix([]byte("footnote")),
+			),
 		),
 		goldmark.WithParserOptions(
 			parser.WithAutoHeadingID(),

appview/pages/markup/sanitizer.go

···
 
 	// for code blocks
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(`chroma`)).OnElements("pre")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`anchor|footnote-ref|footnote-backref`)).OnElements("a")
 	policy.AllowAttrs("class").Matching(regexp.MustCompile(strings.Join(slices.Collect(maps.Values(chroma.StandardTypes)), "|"))).OnElements("span")
 
 	// centering content

input.css

···
 
         .prose li:has(input) {
           list-style: none;
+        .prose a.footnote-backref {
+          @apply no-underline;
         }
 
         .prose li {