fix(html): match vimwiki export output for headings, code fences, tags, anchors (#6)

Exported HTML diverged from upstream vimwiki's :VimwikiAll2HTML in ways
that break custom templates' CSS/JS and deep-links. Bring the renderer to
parity on the structural differences reported in #6:

1. Headings — restore vimwiki's structure: a wrapping
   `<div id="{hierarchical}">` (parent anchors joined by `-`),
   `class="header"`, and an in-heading `<a href="#{hierarchical}">`
   self-link. The flat `id` stays on the heading element so intra-page
   TOC / `#anchor` links keep resolving. Ancestor path is tracked while
   walking top-level headings.

2. Code fences — emit vimwiki's `<pre {raw-attrs}>` (the verbatim text
   after `{{{`, e.g. `<pre python>`) instead of
   `<pre><code class="language-X">`, so highlighters wired for vimwiki
   output apply. The fence text is now preserved verbatim through the
   lexer/AST (PreformattedNode.attrs).

3. Inline tag ids — drop the `tag-` prefix (`id="wiki"`, not
   `id="tag-wiki"`). Also fixes a real inconsistency: the LSP validated
   `[[Page#wiki]]` as resolvable while the HTML emitted `id="tag-wiki"`,
   so the exported link was broken.

4. Same-page anchors — `[[#Section]]` resolves to `index.html#Section`
   (current page filename + fragment), matching vimwiki, rather than a
   bare `#Section`.

Also ship vimwiki's stock style.css verbatim as the default stylesheet
(was a ~7-line minimal one) so exports look identical out of the box and
the `.header`/`.tag`/`.toc`/`done*` classes are styled.

Centered headings and the `<div class="toc">` Contents wrapper keep their
existing form. Tests updated across core + lsp to the new output; added
coverage for hierarchical ids, raw fence attrs, bare tag ids, and the
same-page anchor filename.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/nuwiki-core/tests/html_renderer.rs

@@ -63,7 +63,11 @@ fn heading_levels() {
     for level in 1..=6 {
         let bars = "=".repeat(level);
         let out = render(&format!("{bars} Title {bars}\n"));
-        assert!(out.starts_with(&format!("<h{level} id=\"Title\">Title</h{level}>")));
+        // vimwiki structure: <div id="hier"><h{l} id="flat" class="header">
+        // <a href="#hier">…</a></h{l}></div>. A lone heading has hier == flat.
+        assert!(out.starts_with(&format!(
+            "<div id=\"Title\"><h{level} id=\"Title\" class=\"header\"><a href=\"#Title\">Title</a></h{level}></div>"
+        )), "got: {out}");
     }
 }
 
@@ -94,11 +98,26 @@ fn blockquote_lines_become_paragraphs() {
 }
 
 #[test]
-fn preformatted_block_emits_pre_code_with_language_class() {
+fn preformatted_block_emits_pre_with_raw_fence_attrs() {
+    // vimwiki drops the verbatim fence text into the <pre> tag (`{{{rust` →
+    // `<pre rust>`), with no inner <code> wrapper.
     let out = render("{{{rust\nfn main() {}\n}}}\n");
-    assert!(out.contains("<pre><code class=\"language-rust\">"));
+    assert!(out.contains("<pre rust>"), "got: {out}");
     assert!(out.contains("fn main() {}"));
-    assert!(out.contains("</code></pre>"));
+    assert!(out.contains("</pre>"));
+    assert!(!out.contains("<code"), "no inner code element: {out}");
+}
+
+#[test]
+fn preformatted_block_without_attrs_is_bare_pre() {
+    let out = render("{{{\nplain\n}}}\n");
+    assert!(out.contains("<pre>plain"), "got: {out}");
+}
+
+#[test]
+fn preformatted_block_keeps_full_attr_string() {
+    let out = render("{{{class=\"brush: python\"\nx\n}}}\n");
+    assert!(out.contains("<pre class=\"brush: python\">"), "got: {out}");
 }
 
 #[test]
@@ -244,7 +263,10 @@ fn heading_id_matches_anchor_link_href() {
     // for "exported HTML anchor links don't work".
     let out = render("= My Section =\n\n[[#My Section]]\n");
     assert!(
-        out.contains("<h1 id=\"My Section\">My Section</h1>"),
+        out.contains(
+            "<div id=\"My Section\"><h1 id=\"My Section\" class=\"header\">\
+             <a href=\"#My Section\">My Section</a></h1></div>"
+        ),
         "heading id: {out}"
     );
     assert!(
@@ -276,7 +298,13 @@ fn non_toc_heading_not_wrapped() {
         .with_toc_header("Contents")
         .render_to_string(&doc)
         .unwrap();
-    assert!(out.contains("<h2 id=\"Intro\">Intro</h2>"), "got: {out}");
+    assert!(
+        out.contains(
+            "<div id=\"Intro\"><h2 id=\"Intro\" class=\"header\">\
+             <a href=\"#Intro\">Intro</a></h2></div>"
+        ),
+        "got: {out}"
+    );
     assert!(!out.contains("class=\"toc\""), "got: {out}");
 }
 
@@ -342,7 +370,7 @@ fn template_substitutes_content_and_title() {
     );
     let out = renderer.render_to_string(&doc).unwrap();
     assert!(out.contains("<title>My Page</title>"));
-    assert!(out.contains("<body><h1 id=\"Hello\">Hello</h1>"));
+    assert!(out.contains("<body><div id=\"Hello\"><h1 id=\"Hello\" class=\"header\"><a href=\"#Hello\">Hello</a></h1></div>"));
 }
 
 #[test]
@@ -351,7 +379,7 @@ fn template_with_missing_title_substitutes_empty_string() {
     let renderer = HtmlRenderer::new().with_template("<title>{{title}}</title>{{content}}");
     let out = renderer.render_to_string(&doc).unwrap();
     assert!(out.contains("<title></title>"));
-    assert!(out.contains("<h1 id=\"Heading\">Heading</h1>"));
+    assert!(out.contains("<div id=\"Heading\"><h1 id=\"Heading\" class=\"header\"><a href=\"#Heading\">Heading</a></h1></div>"));
 }
 
 #[test]
@@ -367,7 +395,7 @@ fn template_substitutes_vimwiki_percent_placeholders() {
     let out = renderer.render_to_string(&doc).unwrap();
     assert!(out.contains("<title>My Page</title>"), "title: {out}");
     assert!(
-        out.contains("<body><h1 id=\"Hello\">Hello</h1>"),
+        out.contains("<body><div id=\"Hello\"><h1 id=\"Hello\" class=\"header\"><a href=\"#Hello\">Hello</a></h1></div>"),
         "content: {out}"
     );
     assert!(out.contains("href=\"../style.css\""), "root_path: {out}");
@@ -461,7 +489,7 @@ fn x() {}
     let out = HtmlRenderer::new().render_to_string(&doc).unwrap();
     // A few sanity checks; the full output is exercised piece-by-piece above.
     for needle in [
-        "<h1 id=\"Heading\">Heading</h1>",
+        "<div id=\"Heading\"><h1 id=\"Heading\" class=\"header\"><a href=\"#Heading\">Heading</a></h1></div>",
         "<strong>bold</strong>",
         "<em>italic</em>",
         "<code>code</code>",
@@ -469,7 +497,7 @@ fn x() {}
         "<blockquote>",
         "<hr>",
         "<table>",
-        "<pre><code class=\"language-rust\">",
+        "<pre rust>",
     ] {
         assert!(
             out.contains(needle),