feat(config): configurable generated-section captions (P2)

TOC / links / tags section headings (and their levels) were hardcoded.
Added per-wiki toc_header/toc_header_level, links_header/links_header_level,
tags_header/tags_header_level — defaults Contents / Generated Links /
Generated Tags at level 1, matching upstream (also fixes the tags index
heading: Tags -> Generated Tags).

A caption_line(name, level) helper emits the `=`-markers; the configured
text + level thread through toc_edit / links_edit / tag_links_edit and the
auto_toc save hook. find_section_range matches the configured text, so
regeneration stays idempotent at any level.

Tests: captions_honour_custom_header_and_level (link_health) + config
round-trip + default assertions (index_and_config); existing tag/toc/links
tests updated for the new arity and the Generated Tags default. fmt/clippy
clean (8-arg ops get allow(too_many_arguments), matching the codebase
precedent); 0 Rust test failures; config-parity green.

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

crates/nuwiki-lsp/tests/index_and_config.rs

@@ -275,6 +275,12 @@ fn defaults_carry_vimwiki_per_wiki_keys() {
     assert_eq!(cfg.list_margin, -1);
     assert_eq!(cfg.links_space_char, " ");
     assert!(!cfg.auto_toc);
+    // Generated-section captions match upstream defaults.
+    assert_eq!(cfg.toc_header, "Contents");
+    assert_eq!(cfg.toc_header_level, 1);
+    assert_eq!(cfg.links_header, "Generated Links");
+    assert_eq!(cfg.tags_header, "Generated Tags");
+    assert_eq!(cfg.listsym_rejected, "-");
 }
 
 #[test]
@@ -295,6 +301,11 @@ fn raw_wiki_parses_every_new_key() {
             "list_margin": 2,
             "links_space_char": "_",
             "auto_toc": true,
+            "toc_header": "Table of Contents",
+            "toc_header_level": 2,
+            "links_header": "All Pages",
+            "tags_header": "Tag Index",
+            "tags_header_level": 3,
         }],
     }));
     let w = &cfg.wikis[0];
@@ -312,6 +323,12 @@ fn raw_wiki_parses_every_new_key() {
     assert_eq!(w.list_margin, 2);
     assert_eq!(w.links_space_char, "_");
     assert!(w.auto_toc);
+    assert_eq!(w.toc_header, "Table of Contents");
+    assert_eq!(w.toc_header_level, 2);
+    assert_eq!(w.links_header, "All Pages");
+    assert_eq!(w.links_header_level, 1); // unspecified → default
+    assert_eq!(w.tags_header, "Tag Index");
+    assert_eq!(w.tags_header_level, 3);
 
     // The parsed keys drive a date-mode, Sunday-start diary calendar:
     // a weekly note is the week-start date (YYYY-MM-DD), stepping ±7 days.