feat(html): html_header_numbering section numbering for HTML export

Mirror vimwiki's html_header_numbering / html_header_numbering_sym:
top-level headings at or below the start level get a dotted section
number (1, 1.1, 1.2, ...) with a configurable trailing symbol. Off by
default (level 0). Nested headings in lists/quotes stay unnumbered,
matching upstream's document-level-only scan.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/nuwiki-lsp/src/config.rs

@@ -137,6 +137,12 @@ pub struct HtmlConfig {
     pub custom_wiki2html_args: String,
     /// URL prefix prepended to RSS feed / diary item links (`base_url`).
     pub base_url: String,
+    /// vimwiki `html_header_numbering`: heading level at which automatic
+    /// section numbering starts in HTML export (`0` = off, the default).
+    pub html_header_numbering: u8,
+    /// vimwiki `html_header_numbering_sym`: symbol appended after the
+    /// section number (e.g. `.` → `1.2. Heading`). Empty by default.
+    pub html_header_numbering_sym: String,
 }
 
 impl Default for HtmlConfig {
@@ -155,6 +161,8 @@ impl Default for HtmlConfig {
             custom_wiki2html: String::new(),
             custom_wiki2html_args: String::new(),
             base_url: String::new(),
+            html_header_numbering: 0,
+            html_header_numbering_sym: String::new(),
         }
     }
 }
@@ -650,6 +658,10 @@ struct RawWiki {
     custom_wiki2html_args: Option<String>,
     #[serde(default)]
     base_url: Option<String>,
+    #[serde(default)]
+    html_header_numbering: Option<u8>,
+    #[serde(default)]
+    html_header_numbering_sym: Option<String>,
     // per-wiki keys mirroring vimwiki globals. All optional so
     // existing single-wiki configs migrate without touching anything.
     #[serde(default)]
@@ -745,6 +757,12 @@ impl From<RawWiki> for WikiConfig {
         if let Some(s) = r.base_url {
             html.base_url = s;
         }
+        if let Some(n) = r.html_header_numbering {
+            html.html_header_numbering = n;
+        }
+        if let Some(s) = r.html_header_numbering_sym {
+            html.html_header_numbering_sym = s;
+        }
         let d = wiki_defaults();
         WikiConfig {
             name: r.name.unwrap_or(derived_name),

crates/nuwiki-lsp/src/export.rs

@@ -252,6 +252,12 @@ pub fn render_page_html(
     if !cfg.color_dic.is_empty() {
         r = r.with_colors(cfg.color_dic.clone());
     }
+    if cfg.html_header_numbering > 0 {
+        r = r.with_header_numbering(
+            cfg.html_header_numbering,
+            cfg.html_header_numbering_sym.clone(),
+        );
+    }
     r.render_to_string(doc)
 }