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>

development/vimwiki-gap.md

@@ -87,9 +87,17 @@ fix site.
   `<Leader>w<Leader>m` stays tomorrow — exact upstream parity
   (`lua/nuwiki/keymaps.lua`, `ftplugin/vimwiki.vim`; docs + README updated).
   Covered by `diary.leader_t_opens_today_in_tab` / `diary.leader_m_opens_tomorrow`.
-- [ ] **Generated-section captions hardcoded** — `toc_header` /
-  `toc_header_level`, `links_header`, `tags_header` (+levels).
-  _Fix:_ `crates/nuwiki-lsp/src/config.rs` + server TOC/generate renderers.
+- [x] **Generated-section captions hardcoded** — TOC/links/tags headings and
+  their levels were hardcoded (`= Contents =`, `= Generated Links =`, `= Tags =`,
+  all level 1). _Fix:_ added per-wiki `toc_header`/`toc_header_level`,
+  `links_header`/`links_header_level`, `tags_header`/`tags_header_level`
+  (defaults `Contents`/`Generated Links`/`Generated Tags`, level 1 — matching
+  upstream; this also corrects the tags index heading from `Tags` →
+  `Generated Tags`). A `caption_line(name, level)` helper emits the markers; the
+  text + level thread through `toc_edit`/`links_edit`/`tag_links_edit` (+ the
+  auto_toc save hook) and `find_section_range` matches the configured text so
+  regen stays idempotent. Tests: `captions_honour_custom_header_and_level`
+  (`link_health.rs`) + config round-trip in `index_and_config.rs`.
 - [ ] **On-save autoregen family** — `auto_diary_index`, `auto_generate_links`,
   `auto_generate_tags`, `auto_tags` (only `auto_toc` / `auto_export` exist).
   _Fix:_ `config.rs` `RawWiki`/`WikiConfig` + the `didSave` path.