parity(2): insert-mode list bindings (<C-D>/<C-T>/<C-L><C-?>)

Match upstream vimwiki's insert-mode list editing:
  <C-D>      list_change_level(-1)   dedent current item
  <C-T>      list_change_level(+1)   indent current item
  <C-L><C-J> list_cycle_symbol(+1)   cycle marker forward
  <C-L><C-K> list_cycle_symbol(-1)   cycle marker backward
  <C-L><C-M> list_toggle_or_add_chk  toggle if has checkbox, else add `[ ]`

Cycle order matches vimwiki's canonical run:
  - → * → # → 1. → 1) → a) → A) → i) → I) → (wrap)

Both Lua and VimL paths wired. Lua callbacks fire directly (no `<C-o>`
dance) since list_change_level / changeSymbol mutate the buffer via
the LSP applyEdit pipeline, which works cleanly in insert mode. VimL
keeps the `<C-o>:call …<CR>` idiom since that's the standard there.

Harness adds 5 cases covering the new insert-mode bindings plus one
direct LSP roundtrip for changeSymbol — surfaced a long-standing
stale-binary footgun in test-keymaps.sh (rebuilt only when bin was
missing; now rebuilds every run since incremental cargo is fast).
Harness also captures server log_messages and dumps them on failure
so future swallowed-error bugs (Err → log + Ok(None)) are visible.

Gates: 421 Rust / 25 Neovim / 12 Vim.

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

lua/nuwiki/commands.lua

@@ -515,6 +515,73 @@ function M.list_change_lvl(direction)
   M.list_change_level(delta, false)
 end
 
+--- Cycle the list marker forward (`direction = 1`) or backward
+--- (`direction = -1`). Pure client-side: detects the current line's
+--- marker via regex, picks the next symbol in vimwiki's canonical
+--- order, and dispatches `list.changeSymbol`.
+local _symbol_order = { '-', '*', '#', '1.', '1)', 'a)', 'A)', 'i)', 'I)' }
+
+local function detect_current_symbol()
+  local line = vim.api.nvim_get_current_line()
+  -- Match optional indent, marker, then whitespace.
+  local indent, marker = line:match('^(%s*)([%-%*%#]) ')
+  if marker then return marker end
+  local n
+  indent, n, marker = line:match('^(%s*)(%d+)([%.%)]) ')
+  if marker then return '1' .. marker end
+  -- Roman lower
+  indent, marker = line:match('^(%s*)([ivxlcdm]+)%) ')
+  if marker then return 'i)' end
+  -- Roman upper
+  indent, marker = line:match('^(%s*)([IVXLCDM]+)%) ')
+  if marker then return 'I)' end
+  -- Alpha lower (single letter or short run)
+  indent, marker = line:match('^(%s*)([a-z]+)%) ')
+  if marker then return 'a)' end
+  indent, marker = line:match('^(%s*)([A-Z]+)%) ')
+  if marker then return 'A)' end
+  -- Suppress unused warning
+  local _ = indent
+  return nil
+end
+
+function M.list_cycle_symbol(direction)
+  local current = detect_current_symbol()
+  if not current then return end
+  local idx
+  for i, s in ipairs(_symbol_order) do
+    if s == current then idx = i break end
+  end
+  if not idx then return end
+  local next_idx = ((idx - 1 + (direction or 1)) % #_symbol_order) + 1
+  M.list_change_symbol(_symbol_order[next_idx], false)
+end
+
+--- `<C-L><C-M>` (insert mode) — toggle the checkbox on the current
+--- item if any, OR insert `[ ]` after the marker if the line is a
+--- plain list item without one. Pure client-side.
+function M.list_toggle_or_add_checkbox()
+  local line = vim.api.nvim_get_current_line()
+  -- Already has a checkbox? Let the server's toggle handle it.
+  if line:match('%s*[%-%*%#]%s+%[[%sxXoO%.%-]%]') or
+     line:match('%s*%w+[%.%)]%s+%[[%sxXoO%.%-]%]') then
+    M.toggle_list_item()
+    return
+  end
+  -- Looks like a list item without a checkbox — insert `[ ] ` after
+  -- the marker.
+  local row = vim.api.nvim_win_get_cursor(0)[1]
+  local insert_at = nil
+  local function try(pattern)
+    local start_, finish = line:find(pattern)
+    if start_ then return finish end
+  end
+  insert_at = try('^%s*[%-%*%#] ') or try('^%s*%w+[%.%)] ')
+  if not insert_at then return end
+  local new_line = line:sub(1, insert_at) .. '[ ] ' .. line:sub(insert_at + 1)
+  vim.api.nvim_buf_set_lines(0, row - 1, row, false, { new_line })
+end
+
 -- §13.1 Cluster B — table rewriters.
 
 function M.table_insert(cols, rows)