docs(client): document link-follow commands on both editors + tab-drop

The split/tab link-follow commands are no longer Neovim-only; document
:Nuwiki/Vimwiki{Split,VSplit,Tabnew,TabDrop,GoBack}Link and note that
<C-S-CR> follows a link in a tab reusing an existing one. Tick parity
gap P1 #1 in the tracking doc.

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

doc/nuwiki.txt

@@ -284,6 +284,25 @@ Wiki / navigation ~
 :NuwikiFollowLink
     Follow the link under the cursor.
 
+                                                          *:NuwikiSplitLink*
+:NuwikiSplitLink
+                                                         *:NuwikiVSplitLink*
+:NuwikiVSplitLink
+                                                         *:NuwikiTabnewLink*
+:NuwikiTabnewLink
+    Follow the link under the cursor in a horizontal split, vertical
+    split, or new tab respectively.
+
+                                                        *:NuwikiTabDropLink*
+:NuwikiTabDropLink
+    Follow the link under the cursor in a tab, reusing an existing tab
+    if the target file is already open (otherwise a new tab is created).
+
+                                                         *:NuwikiGoBackLink*
+:NuwikiGoBackLink
+    Jump back to where you followed the link from (via the jumplist,
+    |CTRL-O|).
+
                                                           *:NuwikiBacklinks*
 :NuwikiBacklinks
     Show all references to the current page.
@@ -412,7 +431,8 @@ Links (normal mode) ~
              wraps as `[[word]]` (second <CR> follows the link).
   <S-CR>     Follow in a horizontal split.
   <C-CR>     Follow in a vertical split.
-  <C-S-CR>   Follow in a new tab.
+  <C-S-CR>   Follow in a tab, reusing an existing tab if the file is
+             already open.
   <BS>       Jump back (`<C-o>`).
   <Tab>      Next wikilink on or after the cursor.
   <S-Tab>    Previous wikilink.