docs: fix stale README + help file (audit)

A three-agent audit cross-checked README.md and doc/nuwiki.txt against the
actual config, commands, and mappings in code. Fixes:

Mappings:
- doc/nuwiki.txt wrongly described <Leader>ww as "open today's diary" — it
  opens the wiki index (diary-today is <Leader>w<Leader>w). Corrected, and
  the missing <Leader>wt (wiki index in a tab) row added.
- README feature bullet referenced <Leader>ww for the diary; fixed to
  <Leader>w<Leader>w.
- Both keymap listings now note <Leader>w is the default map_prefix.

Config globals:
- README globals table was missing real, code-read globals: g:nuwiki_syntax,
  g:nuwiki_diary_rel_path, g:nuwiki_wikis, g:nuwiki_map_prefix,
  g:nuwiki_binary_path, g:nuwiki_build_from_source. Added.
- doc/nuwiki.txt globals section gained g:nuwiki_diary_rel_path and
  g:nuwiki_link_severity (both read in autoload but undocumented).
- doc/nuwiki.txt per-wiki list gained template_date_format,
  html_filename_parameterization, color_dic, list_margin (in README only).

Commands:
- doc/nuwiki.txt was missing a whole list/task/table command group plus
  :NuwikiFindOrphans, :NuwikiNormalizeLink, :NuwikiColorize,
  :NuwikiPasteLink/PasteUrl/CatUrl. Added, matching README's descriptions.

No default-value mismatches and no phantom (documented-but-nonexistent)
entries were found. helptags validates with no duplicate tags.

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

README.md

@@ -50,7 +50,7 @@ results.
 
 ### Diary
 
-- Daily diary out of the box (`<Leader>ww`, `<C-Down>` / `<C-Up>`).
+- Daily diary out of the box (`<Leader>w<Leader>w`, `<C-Down>` / `<C-Up>`).
 - Configurable cadence: set `diary_frequency = 'weekly'` (or `'monthly'`
   / `'yearly'`) per wiki and the commands address `2026-W19.wiki`,
   `2026-05.wiki`, `2026.wiki` instead. Navigation stays at the same
@@ -377,8 +377,12 @@ For users configuring without Lua.
 |--------|---------|---------|
 | `g:nuwiki_wiki_root` | `'~/vimwiki'` | single-wiki root |
 | `g:nuwiki_file_extension` | `'.wiki'` | wiki file extension |
+| `g:nuwiki_syntax` | `'vimwiki'` | wiki syntax |
+| `g:nuwiki_diary_rel_path` | `'diary'` | diary subdirectory (relative to the wiki root) |
+| `g:nuwiki_wikis` | _(unset)_ | list of per-wiki dicts for multi-wiki setups; wins over the scalar globals |
 | `g:nuwiki_log_level` | `'warn'` | `error` \| `warn` \| `info` \| `debug` |
 | `g:nuwiki_link_severity` | `'warn'` | broken-link severity: `off` \| `hint` \| `warn` \| `error` |
+| `g:nuwiki_map_prefix` | `'<Leader>w'` | prefix for the wiki command family |
 | `g:nuwiki_no_default_mappings` | `0` | `1` skips the whole keymap layer |
 | `g:nuwiki_no_wiki_prefix_mappings` | `0` | `1` skips the `<Leader>w*` group |
 | `g:nuwiki_no_links_mappings` | `0` | `1` skips the link group (`<CR>`, `+`, …) |
@@ -390,6 +394,8 @@ For users configuring without Lua.
 | `g:nuwiki_no_text_objects_mappings` | `0` | `1` skips the text-object group (`ah`, `il`, …) |
 | `g:nuwiki_no_folding` | `0` | `1` skips foldexpr setup |
 | `g:nuwiki_mouse_mappings` | `0` | `1` enables mouse maps |
+| `g:nuwiki_binary_path` | _(auto)_ | path to a prebuilt `nuwiki-ls` binary, bypassing the bundled one |
+| `g:nuwiki_build_from_source` | `0` | `1` builds the binary with `cargo` instead of downloading a release |
 
 ---
 
@@ -563,6 +569,8 @@ vimwiki) they fire only after `'timeoutlen'`; type a suffix such as `gln` or
 
 **Wiki / diary / export** (normal mode)
 
+The `<Leader>w` prefix below is the default `map_prefix` (`g:nuwiki_map_prefix`); change that option to relocate the whole family.
+
 | Key | Action |
 |---|---|
 | `<Leader>ww` | Open the wiki index |