parity(1): vimwiki per-wiki config keys, table colspan/rowspan,

named link commands, mouse maps

Parity audit Cluster 1 — small wins.

WikiConfig (server) extended with 14 vimwiki globals:
- `index` (`g:vimwiki_index`), wired into `:VimwikiIndex` so users
  with a custom index page stem (e.g. `home`) get the right file.
- `diary_frequency`, `diary_start_week_day`, `diary_caption_level`,
  `diary_sort`, `diary_header` — diary keys (weekly/monthly/yearly
  semantics land in Cluster 4; the keys parse now so config
  migration doesn't need to wait).
- `maxhi`, `listsyms`, `listsyms_propagate`, `list_margin`,
  `links_space_char`, `nested_syntaxes`, `auto_toc` — list +
  highlight knobs the renderer/handlers can consult.

All keys threaded through `RawWiki` → `WikiConfig::from(RawWiki)`,
defaults centralised in `wiki_defaults()` so `empty()`, `from_root()`,
the legacy single-wiki path, and the `RawWiki` impl stay in sync.

Lua front-door (`lua/nuwiki/config.lua`) now documents the multi-wiki
`wikis = {…}` shape with every accepted per-wiki key — users who
prefer Lua tables no longer have to round-trip through
`init_options` raw JSON.

HTML renderer (`crates/nuwiki-core/src/render/html.rs`):
- New `table_spans()` pre-pass resolves vimwiki's `>` (col_span) and
  `\\/` (row_span) continuation markers into proper HTML
  `colspan="N"` / `rowspan="N"` attributes on the lead cell. Continuation
  cells emit nothing, matching what browsers expect.
- The old behaviour (emitting `class="col-span"` / `class="row-span"`
  as visual markers) is gone — replaced with real merging so the
  rendered HTML matches the source semantics.

Named ex-commands:
- `:VimwikiNextLink` / `:VimwikiPrevLink` — were keymapped only
  (`<Tab>`/`<S-Tab>`); now have explicit `:` commands in both editor
  paths, dispatching to new `nuwiki.commands.link_next` / `link_prev`
  pure-Vim/Lua helpers.
- `:VimwikiBaddLink` — adds the link target's file to the buffer
  list without switching focus. Goes through
  `textDocument/definition` and runs `:badd <fname>` on the resolved
  URI.

Mouse maps (opt-in via `mappings.mouse = true` in Lua or
`g:nuwiki_mouse_mappings = 1` in Vim):
- `<2-LeftMouse>` follows, `<S-2-LeftMouse>` / `<C-2-LeftMouse>`
  follow in split/vsplit, `<MiddleMouse>` adds to buflist,
  `<RightMouse>` goes back. Mirrors upstream vimwiki's defaults.

Tests: 7 new in `parity_cluster_1.rs` covering the per-wiki config
defaults + raw JSON parse, the legacy-single-wiki path, colspan
folding into a lead cell with no leftover class markers, rowspan
across rows, no-attrs when the table has no spans, and a sanity
paragraph render. Total 421 Rust tests pass; clippy clean; both
keymap harnesses still green (20 nvim + 12 vim).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

autoload/nuwiki/commands.vim

@@ -94,6 +94,44 @@ function! s:wiki_pick(notification) abort
         \ function('s:open_uri_from'))
 endfunction
 
+" `:VimwikiNextLink` / `:VimwikiPrevLink` — pure-VimL `[[…]]` jumper.
+function! nuwiki#commands#link_next() abort
+  call search('\[\[', 'W')
+endfunction
+function! nuwiki#commands#link_prev() abort
+  call search('\[\[', 'bW')
+endfunction
+
+" `:VimwikiBaddLink` — add the link target file to the buffer list
+" without focus. Routes through vim-lsp's textDocument/definition.
+function! nuwiki#commands#badd_link() abort
+  if !s:has_vimlsp()
+    echohl ErrorMsg | echom 'nuwiki: vim-lsp not loaded' | echohl None
+    return
+  endif
+  call lsp#send_request(s:server, {
+        \ 'method': 'textDocument/definition',
+        \ 'params': s:cursor_position(),
+        \ 'on_notification': function('s:badd_from_response'),
+        \ })
+endfunction
+
+function! s:badd_from_response(notification) abort
+  let l:result = get(get(a:notification, 'response', {}), 'result', {})
+  let l:uri = ''
+  if type(l:result) == type({})
+    let l:uri = get(l:result, 'uri', get(l:result, 'targetUri', ''))
+  elseif type(l:result) == type([]) && !empty(l:result)
+    let l:uri = get(l:result[0], 'uri', get(l:result[0], 'targetUri', ''))
+  endif
+  if l:uri ==# ''
+    return
+  endif
+  let l:path = substitute(l:uri, '^file://', '', '')
+  execute 'badd ' . fnameescape(l:path)
+  echom 'nuwiki: added ' . l:path
+endfunction
+
 " ===== Smart <CR>: follow or wrap-then-follow =====
 
 function! s:cursor_inside_wikilink() abort