feat(config): P3 config batch — group 1 (clean config + plumbing)

Config plumbing for the whole config batch (HtmlConfig + WikiConfig fields,
RawWiki deserialization, From/defaults) plus these behaviors:

- rss_name / rss_max_items: HtmlConfig fields (wired into write_rss in the RSS
  group).
- toc_link_format: build_toc_text emits [[#anchor]] (no description) for 1,
  [[#anchor|title]] for 0.
- generated_links_caption: build_links_text emits [[page|FirstHeading]] from a
  page->heading map (ops::page_captions) when enabled.
- table_reduce_last_col: column_widths clamps the last column to width 1 when
  set; threaded through table_align_edit/table_move_column_edit + commands.
- color_dic now ships a populated default palette (red/green/blue/...).
- commentstring aligned to upstream's no-space `%%%s`.
- auto_chdir (default off): :lcd into the owning wiki root on buffer enter;
  both clients (ftplugin.lua setup_auto_chdir + Vim NuwikiAutoChdir augroup),
  with config.wiki_root_for / nuwiki#commands#wiki_root_for resolvers.

Also seeded HtmlConfig fields for later groups (valid_html_tags,
list/text_ignore_newline, emoji_enable, user_htmls, color_tag_template) and
WikiConfig (create_link, dir_link, bullet_types, cycle_bullets).

Tests: toc_link_format, generated_links_caption, table_reduce_last_col,
config defaults + JSON round-trip for every new key. Full rust suite +
both keymap harnesses green.

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

lua/nuwiki/config.lua

@@ -70,6 +70,10 @@ M.defaults = {
   -- cursor when leaving insert mode.
   table_auto_fmt = true,
 
+  -- vimwiki `auto_chdir` (default off): `:lcd` into the owning wiki's root
+  -- when a wiki buffer becomes current.
+  auto_chdir = false,
+
   -- Broken-link diagnostic severity. Sent to the server, which downgrades
   -- or suppresses the diagnostic accordingly.
   --   'off' | 'hint' | 'warn' | 'error'
@@ -125,4 +129,17 @@ function M.wiki_list()
   return list
 end
 
+-- Absolute root (with trailing slash) of the wiki that owns `path`, or the
+-- first configured wiki as a fallback. Used by auto_chdir + search scoping.
+function M.wiki_root_for(path)
+  for _, w in ipairs(M.wiki_list()) do
+    local wroot = vim.fn.fnamemodify(vim.fn.expand(w.root), ':p')
+    if path:sub(1, #wroot) == wroot then
+      return wroot
+    end
+  end
+  local first = M.wiki_list()[1]
+  return first and vim.fn.fnamemodify(vim.fn.expand(first.root), ':p') or nil
+end
+
 return M

lua/nuwiki/ftplugin.lua

@@ -94,6 +94,31 @@ local function setup_table_auto_fmt(bufnr, enabled)
   })
 end
 
+-- vimwiki `auto_chdir`: `:lcd` into the owning wiki's root while this buffer
+-- is current.
+local function setup_auto_chdir(bufnr, enabled)
+  if not enabled then
+    return
+  end
+  if bufnr == 0 then
+    bufnr = vim.api.nvim_get_current_buf()
+  end
+  local function chdir()
+    local file = vim.api.nvim_buf_get_name(bufnr)
+    local root = require('nuwiki.config').wiki_root_for(file)
+    if root then
+      vim.cmd('lcd ' .. vim.fn.fnameescape(root))
+    end
+  end
+  local grp = vim.api.nvim_create_augroup('nuwiki_chdir_' .. bufnr, { clear = true })
+  vim.api.nvim_create_autocmd({ 'BufEnter', 'BufWinEnter' }, {
+    buffer = bufnr,
+    group = grp,
+    callback = chdir,
+  })
+  chdir()
+end
+
 function M.attach(bufnr)
   bufnr = bufnr or 0
   local config = require('nuwiki.config')
@@ -109,6 +134,7 @@ function M.attach(bufnr)
   setup_folding(bufnr, opts.folding or 'lsp')
   setup_autowriteall(bufnr, opts.autowriteall ~= false)
   setup_table_auto_fmt(bufnr, opts.table_auto_fmt ~= false)
+  setup_auto_chdir(bufnr, opts.auto_chdir == true)
 end
 
 return M