feat(commands): command-line completion for Goto/Colorize/tag commands (P3)

Upstream attaches -complete= to several commands; nuwiki had none, so <Tab>
at the : line never completed page/tag/colour names. New
autoload/nuwiki/complete.vim adds pure client-side, synchronous completers
(config + filesystem, never the LSP — so they work under vim-lsp, coc and
Neovim), wired via -complete=customlist into all command contexts:

- nuwiki#complete#pages → VimwikiGoto/NuwikiGoto (glob wiki roots for page names)
- nuwiki#complete#colors → VimwikiColorize/NuwikiColorize (color_dic keys +
  colours already used in buffer color:… spans)
- nuwiki#complete#tags → VimwikiSearchTags/GenerateTagLinks/GenerateTags (+Nuwiki)
  (scan wiki files for :tag: runs — the tag index is server-side and a
  synchronous completer can't query it, so we read the same source it indexes)

Documented divergence: no file completer for VimwikiRenameFile — nuwiki
delegates renaming to the LSP rename request (no filename arg to complete),
unlike upstream which renames itself.

Tests: complete.{pages_globs_and_filters,tags_scans_wiki_files,
colors_from_buffer_spans} (test-keymaps-vim.vim). Both harnesses green.

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

autoload/nuwiki/complete.vim

@@ -0,0 +1,86 @@
+" autoload/nuwiki/complete.vim — command-line completion for the
+" :Vimwiki*/:Nuwiki* commands (mirrors upstream vimwiki's -complete= specs).
+"
+" Pure client-side and synchronous: candidates come from config and the
+" filesystem, never the LSP, so a `-complete=customlist,{fn}` attribute can
+" call these directly under vim-lsp, coc, and Neovim alike.
+"
+" NOTE on files/RenameFile: upstream's :VimwikiRenameFile takes a new-name arg
+" with file completion because upstream performs the rename itself. nuwiki
+" delegates renaming to the LSP rename request (`:LspRename` / coc `rename`),
+" which drives its own interactive prompt — there is no filename argument to
+" complete, so no file completer is provided (documented divergence).
+
+" Page-name completion (VimwikiGoto). Globs every configured wiki root for its
+" `*<ext>` files and returns their root-relative names with the extension
+" stripped, filtered by {arglead}. Mirrors upstream complete_links_raw.
+function! nuwiki#complete#pages(arglead, cmdline, cursorpos) abort
+  let l:names = {}
+  for l:w in nuwiki#commands#wiki_list()
+    let l:root = substitute(get(l:w, 'root', ''), '/\+$', '', '')
+    if l:root ==# '' | continue | endif
+    let l:ext = get(l:w, 'ext', '.wiki')
+    for l:f in glob(l:root . '/**/*' . l:ext, 0, 1)
+      let l:rel = l:f[len(l:root) + 1 :]
+      if l:rel ==# '' | continue | endif
+      let l:rel = l:rel[: -len(l:ext) - 1]
+      let l:names[l:rel] = 1
+    endfor
+  endfor
+  return filter(sort(keys(l:names)), 'stridx(v:val, a:arglead) == 0')
+endfunction
+
+" Colour completion (VimwikiColorize) — keys from any configured `color_dic`
+" (per-wiki `g:nuwiki_wikis[].color_dic` or the scalar `g:nuwiki_color_dic`)
+" plus colours already used in `color:NAME` spans in the current buffer.
+function! nuwiki#complete#colors(arglead, cmdline, cursorpos) abort
+  let l:set = {}
+  for l:w in get(g:, 'nuwiki_wikis', [])
+    for l:k in keys(get(l:w, 'color_dic', {}))
+      let l:set[l:k] = 1
+    endfor
+  endfor
+  for l:k in keys(get(g:, 'nuwiki_color_dic', {}))
+    let l:set[l:k] = 1
+  endfor
+  for l:line in getline(1, '$')
+    let l:start = 0
+    while 1
+      let l:m = matchstrpos(l:line, 'color:\s*\zs[^"'';)]\+', l:start)
+      if l:m[1] < 0 | break | endif
+      let l:set[trim(l:m[0])] = 1
+      let l:start = l:m[2]
+    endwhile
+  endfor
+  return filter(sort(keys(l:set)), 'stridx(v:val, a:arglead) == 0')
+endfunction
+
+" Tag completion (VimwikiSearchTags / VimwikiGenerateTagLinks). The tag index
+" lives in the LSP server, which a synchronous completer can't query, so we
+" harvest `:tag:` tokens by scanning the configured wikis' files directly —
+" the same source the server indexes. Runs only on <Tab> at the `:` line.
+function! nuwiki#complete#tags(arglead, cmdline, cursorpos) abort
+  let l:set = {}
+  for l:w in nuwiki#commands#wiki_list()
+    let l:root = substitute(get(l:w, 'root', ''), '/\+$', '', '')
+    if l:root ==# '' | continue | endif
+    let l:ext = get(l:w, 'ext', '.wiki')
+    for l:f in glob(l:root . '/**/*' . l:ext, 0, 1)
+      for l:line in readfile(l:f)
+        " Tags come in colon-delimited runs like `:foo:bar:` (no spaces).
+        " Match a whole run, then split out each tag (adjacent tags share a
+        " colon, so a per-tag scan would miss every other one).
+        let l:start = 0
+        while 1
+          let l:m = matchstrpos(l:line, ':\%([^:[:space:]]\+:\)\+', l:start)
+          if l:m[1] < 0 | break | endif
+          for l:t in split(l:m[0], ':')
+            if l:t !=# '' | let l:set[l:t] = 1 | endif
+          endfor
+          let l:start = l:m[2]
+        endwhile
+      endfor
+    endfor
+  endfor
+  return filter(sort(keys(l:set)), 'stridx(v:val, a:arglead) == 0')
+endfunction