Fix glp backward cycle and gl<Space> current-list scope

Two documented checkbox-list mappings did not match their spec:

- `glp` dispatched the same forward-only cycleCheckbox as `gln`, so it
  could never "cycle the checkbox state backward". Add `ops::cycle_state_back`
  and thread a `reverse` flag through the dispatcher and both clients.

- `gl<Space>` and `gL<Space>` both swept the whole buffer, making them
  identical. `gl<Space>` now passes the cursor position and the server
  scopes deletion to the contiguous list block under the cursor (current
  list, cascading into sublists); `gL<Space>` stays whole-buffer.

Adds Rust unit tests, plus behavioral and full-registration coverage for
the documented mapping surface in the Neovim and Vim keymap harnesses, and
a command-coverage suite mirroring the doc's command groups.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/test-keymaps.sh

@@ -38,7 +38,9 @@ cat > "$INIT" <<EOF
 -- Keep the harness self-contained; no plugin manager required.
 vim.opt.runtimepath:prepend('$REPO_ROOT')
 vim.g.nuwiki_binary_path = '$BIN'
-require('nuwiki').setup({ wiki_root = '$TMP/wiki' })
+-- Enable the opt-in mouse mappings so the harness can assert the full
+-- documented mapping surface (doc §6 mouse group).
+require('nuwiki').setup({ wiki_root = '$TMP/wiki', mappings = { mouse = true } })
 EOF
 
 RESULTS="$TMP/results.txt"