fix(lsp): match wikilink anchors against raw heading text

`[[Page#Heading text]]` parsed the anchor as the literal string after
`#`, but the index stored each heading's anchor as `slugify(title)`.
The two never compared equal, so every TOC-style anchor link
(`[[#1. Topologia atual]]`, etc.) was reported as a broken anchor and
goto-definition couldn't jump to the right heading either.

Slugify the request before comparing — `slugify` is idempotent on
valid-slug input, so the same code path now accepts both
`[[Page#some-heading]]` (slug form) and `[[Page#Some Heading]]`
(raw text). Applied to diagnostics, navigation, and hover preview so
all three agree on what "an anchor matches a heading" means.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/nuwiki-lsp/src/lib.rs

@@ -1386,7 +1386,7 @@ fn heading_range_in(idx: &WorkspaceIndex, uri: &Url, anchor: &str, _utf8: bool)
     let page = idx.page(uri)?;
     // Headings win over tags when both match — same precedence as
     // vimwiki: heading anchors are the "canonical" target shape.
-    if let Some(h) = page.headings.iter().find(|h| h.anchor == anchor) {
+    if let Some(h) = page.find_heading_by_anchor(anchor) {
         return Some(span_to_lsp_range_no_text(&h.span));
     }
     // Phase 12: tags-as-anchors. `[[Page#tag-name]]` lands on the
@@ -1434,7 +1434,7 @@ fn preview_for(page: &IndexedPage, anchor: Option<&str>) -> String {
     buf.push_str(title);
     buf.push_str("**\n\n");
     if let Some(anchor) = anchor {
-        if let Some(h) = page.headings.iter().find(|h| h.anchor == anchor) {
+        if let Some(h) = page.find_heading_by_anchor(anchor) {
             buf.push_str(&format!("§ {}\n", h.title));
         } else {
             buf.push_str(&format!("(anchor `{anchor}` not found)\n"));