fix(client): P2 diary tab collision + <M-CR> badd-link parity

Two upstream-parity keymap fixes (confirmed against upstream
ftplugin/vimwiki.vim):

1. <Leader>w<Leader>t collision — nuwiki bound both <Leader>w<Leader>t and
   <Leader>w<Leader>m to tomorrow's diary. Upstream: <Leader>w<Leader>t opens
   today's diary in a NEW TAB, <Leader>w<Leader>m opens tomorrow. <Leader>w
   <Leader>t now calls diary_today_tab; <Leader>w<Leader>m stays tomorrow.

2. <M-CR> badd-link — adding a link target to the buffer list was mouse-only
   (<MiddleMouse>) / command-only (:VimwikiBaddLink). Upstream binds
   <M-CR> -> VimwikiBaddLink. Added normal-mode <M-CR> -> badd_link to the
   links group of both clients.

Both clients (lua/nuwiki/keymaps.lua, ftplugin/vimwiki.vim); README + doc/
nuwiki.txt updated. Tests: map[n].<M-CR> in both harnesses;
diary.leader_t_opens_today_in_tab / diary.leader_m_opens_tomorrow (vim).
nvim 270, vim 263+18, all green.

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

development/tests/test-keymaps-vim.vim

@@ -184,6 +184,7 @@ endfunction
 
 let s:mapping_surface = [
       \ ['<CR>', 'n'], ['<S-CR>', 'n'], ['<C-CR>', 'n'], ['<C-S-CR>', 'n'],
+      \ ['<M-CR>', 'n'],
       \ ['<BS>', 'n'], ['<Tab>', 'n'], ['<S-Tab>', 'n'], ['+', 'nx'],
       \ ['<C-Space>', 'nx'], ['<C-@>', 'nx'], ['<Nul>', 'nx'],
       \ ['gnt', 'n'], ['gln', 'nx'], ['glp', 'nx'], ['glx', 'nx'],
@@ -221,6 +222,18 @@ for s:entry in s:mapping_surface
   endfor
 endfor
 
+" ===== Diary <Leader>w<Leader>{t,m} target (collision fix) =====
+" Upstream: <Leader>w<Leader>t = today in a new tab, <Leader>w<Leader>m =
+" tomorrow. nuwiki used to bind both to tomorrow.
+call s:record(
+      \ maparg('<Leader>w<Leader>t', 'n') =~# 'diary_today_tab' ? 1 : 0,
+      \ 'diary.leader_t_opens_today_in_tab',
+      \ 'rhs=' . maparg('<Leader>w<Leader>t', 'n'))
+call s:record(
+      \ maparg('<Leader>w<Leader>m', 'n') =~# 'diary_tomorrow' ? 1 : 0,
+      \ 'diary.leader_m_opens_tomorrow',
+      \ 'rhs=' . maparg('<Leader>w<Leader>m', 'n'))
+
 " ===== Header nav (pure VimL) =====
 
 call s:run('headers.]]_jumps_to_next', {

development/tests/test-keymaps.lua

@@ -206,6 +206,7 @@ vim.defer_fn(function()
   local mapping_surface = {
     -- Links
     { '<CR>', 'n' }, { '<S-CR>', 'n' }, { '<C-CR>', 'n' }, { '<C-S-CR>', 'n' },
+    { '<M-CR>', 'n' },
     { '<BS>', 'n' }, { '<Tab>', 'n' }, { '<S-Tab>', 'n' }, { '+', 'nx' },
     -- Lists
     { '<C-Space>', 'nx' }, { '<C-@>', 'nx' }, { '<Nul>', 'nx' },