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-lsp/src/config.rs

@@ -12,7 +12,7 @@
 use std::path::{Path, PathBuf};
 
 use serde::Deserialize;
-use tower_lsp::lsp_types::{InitializeParams, Url};
+use tower_lsp::lsp_types::InitializeParams;
 
 #[derive(Debug, Clone, Default)]
 pub struct Config {
@@ -198,9 +198,11 @@ pub struct HtmlConfig {
     /// vimwiki `user_htmls`: basenames of HTML files with no wiki source that
     /// `allToHtml` must not prune. Empty by default.
     pub user_htmls: Vec<String>,
-    /// vimwiki `color_tag_template`: HTML template for a colour span. The
-    /// `__COLORFG__` / `__COLORBG__` / `__CONTENT__` placeholders are filled
-    /// from `color_dic`. Default matches upstream's `<span style=…>` template.
+    /// vimwiki `color_tag_template`: HTML template for a colour span whose name
+    /// resolves in `color_dic`. `__STYLE__` expands to the inline style
+    /// (`color:<css>`) and `__CONTENT__` to the rendered inner HTML. Default
+    /// matches upstream's `<span style="…">…</span>` template. Consumed by
+    /// `HtmlRenderer::render_color`.
     pub color_tag_template: String,
 }
 
@@ -1070,6 +1072,3 @@ pub fn config_from_json(value: serde_json::Value) -> Config {
     cfg.apply_change(&value);
     cfg
 }
-
-#[allow(dead_code)]
-fn _ensure_url_is_used(_u: &Url) {}