dev: exercise toc_header_level + html numbering in the dev launchers

The start-* dev harnesses generated a minimal server config (wiki_root,
file_extension, syntax, log_level, diagnostic) with no display settings,
so :NuwikiTOC always produced `= Contents =` (level 1) regardless of code
changes — there was no way to test toc_header_level/html numbering through
the harness. The coc launcher is worst: coc reads coc-settings.json
verbatim, bypassing the Vim client's config translation entirely.

Set toc_header_level=2, html_header_numbering=2, html_header_numbering_sym
in all three launchers:
- start-vim-coc.sh: into the generated coc-settings.json (init + settings).
- start-vim.sh: as g:nuwiki_* globals (folded into the wiki via the global
  shorthand).
- start-nvim.sh: in the setup() table.

Now the dev wiki demonstrates the settings: :NuwikiTOC writes
`== Contents ==` and HTML export numbers headings.

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

development/start-nvim.sh

@@ -64,6 +64,12 @@ vim.g.nuwiki_diary_rel_path = 'diary'
 
 require('nuwiki').setup({
   wiki_root = '$WIKI_DIR',
+  -- Exercise the per-wiki display settings via the global shorthand: these
+  -- fold into the single wiki, so :NuwikiTOC writes `== Contents ==` (level 2)
+  -- and HTML export numbers headings.
+  toc_header_level = 2,
+  html_header_numbering = 2,
+  html_header_numbering_sym = ' -',
 })
 
 -- Surface log lines (the LSP logs via window/logMessage). Without this