fix(review): close all 2026-06-03 codebase-review findings (R1-R18)

Resolves the 18 findings from the parallel codebase review, tracked in
development/vimwiki-gap.md.

Correctness / perf:
- Wiki.config -> Arc<WikiConfig> so cloning a Wiki is a refcount bump (R5)
- WorkspaceIndex::remove is no longer O(n^2): a per-source contributions
  map limits the scan to buckets the source actually wrote into (R6)
- render_color now expands color_tag_template (__STYLE__/__CONTENT__),
  consuming the previously-dead field; ColorNode documented as an
  extension point; 3 renderer tests added (R3/R4)
- wiki_root_for returns empty/nil on no-match instead of falling back to
  the first wiki (R2); auto_header honours links_space_char (R7)

Cleanup / dedup:
- Remove dead #[allow(dead_code)] stubs + uncalled pub helpers, narrow
  imports (R10/R11)
- Dedup span_of_inline x3 -> InlineNode::span() (R12)
- diary_step single read lock; page_captions single pass (R13)
- Lua auto_header loop -> wiki_list(); detect_current_symbol cleanup
  (R14/R18)

Client / docs:
- :VimwikiNormalizeLink Vim cmds -> <q-args> (R17); ftplugin header fix
  (R16); vars.vim multi-wiki limitation documented (R15)
- Document 19 config options in README.md + doc/nuwiki.txt; fix
  list_margin/shiftwidth doc and stale comments (R1/R9)
- R8 investigated, confirmed not a real bug (documented)

Verified: Neovim harness 307, Vim harness 301/18/21, Rust suite 568, all
0 failed; clippy clean; fresh parallel-agent audit found no regressions.

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

crates/nuwiki-core/src/render/html.rs

@@ -46,6 +46,11 @@ pub struct HtmlRenderer {
     /// names fall through to the default `class="color-<name>"`
     /// rendering. Matches vimwiki's `color_dic`.
     colors: HashMap<String, String>,
+    /// vimwiki `color_tag_template`: the HTML emitted for a colour span whose
+    /// name resolves in `colors`. `__STYLE__` expands to the inline style
+    /// (`color:<css>`) and `__CONTENT__` to the rendered inner HTML. The
+    /// default matches upstream's `<span style="…">…</span>`.
+    color_template: String,
     /// vimwiki `html_header_numbering`: the heading level at which automatic
     /// section numbering begins (`0` = off, the default). When `>= 1`, every
     /// heading at that level or deeper is prefixed with a dotted section
@@ -82,6 +87,7 @@ impl HtmlRenderer {
             template: None,
             vars: HashMap::new(),
             colors: HashMap::new(),
+            color_template: "<span style=\"__STYLE__\">__CONTENT__</span>".to_string(),
             header_numbering: 0,
             header_numbering_sym: String::new(),
             valid_html_tags: Vec::new(),
@@ -156,6 +162,18 @@ impl HtmlRenderer {
         self
     }
 
+    /// Override the colour-span template (vimwiki `color_tag_template`).
+    /// `__STYLE__` is replaced with the resolved `color:<css>` style and
+    /// `__CONTENT__` with the rendered inner HTML. An empty string keeps the
+    /// built-in default.
+    pub fn with_color_template(mut self, template: impl Into<String>) -> Self {
+        let template = template.into();
+        if !template.is_empty() {
+            self.color_template = template;
+        }
+        self
+    }
+
     /// Enable vimwiki-style HTML section numbering. `level` is the heading
     /// level at which numbering starts (`0` disables it); `sym` is appended
     /// after the number. Mirrors `html_header_numbering` /
@@ -311,7 +329,11 @@ impl HtmlRenderer {
 
     fn render_paragraph(&self, n: &ParagraphNode, w: &mut dyn Write) -> io::Result<()> {
         w.write_all(b"<p>")?;
-        let sb = if self.text_ignore_newline { " " } else { "<br />" };
+        let sb = if self.text_ignore_newline {
+            " "
+        } else {
+            "<br />"
+        };
         self.render_inlines_break(&n.children, sb, w)?;
         w.write_all(b"</p>\n")
     }
@@ -389,7 +411,11 @@ impl HtmlRenderer {
             }
             None => w.write_all(b"<li>")?,
         }
-        let sb = if self.list_ignore_newline { " " } else { "<br />" };
+        let sb = if self.list_ignore_newline {
+            " "
+        } else {
+            "<br />"
+        };
         self.render_inlines_break(&n.children, sb, w)?;
         if let Some(sublist) = &n.sublist {
             w.write_all(b"\n")?;
@@ -664,17 +690,32 @@ impl HtmlRenderer {
     }
 
     fn render_color(&self, n: &ColorNode, w: &mut dyn Write) -> io::Result<()> {
+        // Render the inner content up front so it can be slotted into the
+        // colour template.
+        let mut content = Vec::new();
+        self.render_inlines(&n.children, &mut content)?;
+        let content = String::from_utf8_lossy(&content);
+
         if let Some(css) = self.colors.get(&n.color) {
-            w.write_all(b"<span style=\"color:")?;
-            write_escaped(css, w)?;
-            w.write_all(b"\">")?;
+            // Known colour name: expand `color_tag_template` with the resolved
+            // inline style and rendered content.
+            let mut style = b"color:".to_vec();
+            write_escaped(css, &mut style)?;
+            let style = String::from_utf8_lossy(&style);
+            let html = self
+                .color_template
+                .replace("__STYLE__", &style)
+                .replace("__CONTENT__", &content);
+            w.write_all(html.as_bytes())
         } else {
+            // Unknown name: fall back to a class hook the stylesheet can target
+            // (the template only models the inline-style case).
             w.write_all(b"<span class=\"color-")?;
             write_escaped(&n.color, w)?;
             w.write_all(b"\">")?;
+            w.write_all(content.as_bytes())?;
+            w.write_all(b"</span>")
         }
-        self.render_inlines(&n.children, w)?;
-        w.write_all(b"</span>")
     }
 
     fn render_wikilink(&self, n: &WikiLinkNode, w: &mut dyn Write) -> io::Result<()> {