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>

lua/nuwiki/commands.lua

@@ -165,6 +165,47 @@ end
 ---   3. Press inside an existing `[[…]]` follows immediately.
 --- "Not on a word" falls through to plain definition so users can
 --- still chord a definition request anywhere.
+--- Jump to the next / previous `[[…]]` on or after the cursor.
+--- Public so `:VimwikiNextLink` / `:VimwikiPrevLink` can call it.
+local function jump_link(direction)
+  local flags = direction > 0 and 'W' or 'bW'
+  local pos = vim.fn.searchpos([[\[\[]], flags)
+  if pos[1] > 0 then
+    vim.api.nvim_win_set_cursor(0, { pos[1], pos[2] - 1 })
+  end
+end
+function M.link_next() jump_link(1) end
+function M.link_prev() jump_link(-1) end
+
+--- `:VimwikiBaddLink` — add the link target's file to the buffer list
+--- (`:badd`) without switching to it. Uses the LSP definition response
+--- to find the file.
+function M.badd_link()
+  local client = find_client()
+  if not client then
+    vim.notify('nuwiki: language server not attached', vim.log.levels.ERROR)
+    return
+  end
+  local params = position_params(client)
+  params.textDocument = { uri = buf_uri() }
+  local req = client.request
+  local handler = function(_, result)
+    local loc
+    if type(result) == 'table' then
+      loc = result[1] or result
+    end
+    local uri = type(loc) == 'table' and (loc.uri or loc.targetUri) or nil
+    if not uri then return end
+    local path = vim.uri_to_fname(uri)
+    pcall(vim.cmd, 'badd ' .. vim.fn.fnameescape(path))
+    vim.notify('nuwiki: added ' .. path, vim.log.levels.INFO)
+  end
+  local bufnr = vim.api.nvim_get_current_buf()
+  if type(req) == 'function' then
+    client:request('textDocument/definition', params, handler, bufnr)
+  end
+end
+
 function M.follow_link_or_create()
   if cursor_inside_wikilink() then
     vim.lsp.buf.definition()