fix(export): correct list nesting, marks, line-start escaping, svg type

Four export-correctness fixes intermingled across the Typst and EPUB
renderers:

- H7: neutralize newlines in escaped text and apply leading-marker
  escaping (= - + / and N.) to the first text node of every block
  (paragraph, heading, list item, blockquote) and figure captions, even
  when that run carries a mark, so author text can never inject Typst
  markup or phantom headings/TOC entries.
- H9: render lists recursively so nested lists survive and multi-
  paragraph list items keep their paragraph breaks (Typst functional
  list()/enum(); EPUB nested <ul>/<ol> and multiple <p> in <li>).
- H10: render strike, underline and inline code marks in both exporters
  (Typst #strike/#underline/#raw; EPUB <s>/<u>/<code> with css).
- H8b: normalize +-bearing image subtypes so an imported svg+xml cover
  becomes cover.svg with the correct media type.

Validated the generated Typst constructs compile with typst 0.15.

Claude-Session: https://claude.ai/code/session_01RzTWrLiy4zGuw2hZSQGamk

src/export/epub.ts

@@ -25,7 +25,7 @@ function slug(text: string): string {
 
 function imageExtension(dataUrl: string): string {
   const match = /^data:image\/([a-z0-9.+-]+)/i.exec(dataUrl);
-  const kind = (match?.[1] ?? "png").toLowerCase();
+  const kind = (match?.[1] ?? "png").toLowerCase().split("+")[0];
   return kind === "jpeg" ? "jpg" : kind;
 }
 
@@ -42,8 +42,11 @@ function inline(node: JSONContent): string {
   if (node.type === "text") {
     let text = esc(node.text ?? "");
     const marks = node.marks ?? [];
+    if (marks.some((m) => m.type === "code")) text = `<code>${text}</code>`;
     if (marks.some((m) => m.type === "bold")) text = `<strong>${text}</strong>`;
     if (marks.some((m) => m.type === "italic")) text = `<em>${text}</em>`;
+    if (marks.some((m) => m.type === "strike")) text = `<s>${text}</s>`;
+    if (marks.some((m) => m.type === "underline")) text = `<u>${text}</u>`;
     const href = marks.find((m) => m.type === "link")?.attrs?.href;
     if (href) text = `<a href="${attr(href)}">${text}</a>`;
     return text;
@@ -56,11 +59,11 @@ function inlines(content: JSONContent[] = []): string {
   return content.map(inline).join("");
 }
 
-function listItem(item: JSONContent): string {
+function listItem(item: JSONContent, paths: Map<string, string>): string {
   const inner = (item.content ?? [])
-    .filter((c) => c.type === "paragraph")
-    .map((p) => inlines(p.content))
-    .join(" ");
+    .map((child) => block(child, paths))
+    .filter((s) => s.length > 0)
+    .join("");
   return `<li>${inner}</li>`;
 }
 
@@ -92,9 +95,9 @@ function block(node: JSONContent, paths: Map<string, string>): string {
     case "blockquote":
       return `<blockquote>${(node.content ?? []).map((n) => block(n, paths)).join("")}</blockquote>`;
     case "bulletList":
-      return `<ul>${(node.content ?? []).map(listItem).join("")}</ul>`;
+      return `<ul>${(node.content ?? []).map((li) => listItem(li, paths)).join("")}</ul>`;
     case "orderedList":
-      return `<ol>${(node.content ?? []).map(listItem).join("")}</ol>`;
+      return `<ol>${(node.content ?? []).map((li) => listItem(li, paths)).join("")}</ol>`;
     case "horizontalRule":
       return `<hr class="scene-break"/>`;
     case "figure":
@@ -406,6 +409,11 @@ h2, h3 {
   margin: 0;
 }
 
+code {
+  font-family: "SF Mono", Menlo, Consolas, monospace;
+  font-size: 0.9em;
+}
+
 blockquote {
   margin: 1.2em 1.6em;
   font-style: italic;