fix(highlight): complete markdown syntax highlighting with injections

Fix markdown code block highlighting to properly support both markdown
structure (headings, frontmatter) and language injection (rust, bash).

The key fix uses `#set! injection.include-children` in the injection
query to override tree-sitter-md's internal tokenization, enabling
proper highlighting of embedded languages within code fences.

Changes:
- Use crate's HIGHLIGHT_QUERY_BLOCK for base markdown highlighting
- Add custom injection query with include-children directive
- Add YAML/TOML frontmatter and HTML block injection rules
- Add text.* highlight names (title, literal, uri, reference)
- Add string.escape highlight name
- Add CSS styles for new highlight classes
- Remove unused custom md-highlights.scm

docs/static/style.css

@@ -208,6 +208,29 @@ pre code {
   color: #ff79c6;
 }
 
+/* Markdown-specific text highlighting */
+.hl-text-title {
+  color: #ff79c6;
+  font-weight: bold;
+}
+
+.hl-text-literal {
+  color: #8be9fd;
+}
+
+.hl-text-uri {
+  color: #8be9fd;
+  text-decoration: underline;
+}
+
+.hl-text-reference {
+  color: #bd93f9;
+}
+
+.hl-string-escape {
+  color: #ffb86c;
+}
+
 /* Section navigation */
 .section-nav {
   display: flex;