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>

README.md

@@ -366,9 +366,8 @@ also call the server directly with `:CocCommand nuwiki.<command>`.
 
 Only the legacy short forms `:VWB` / `:VWS` and `:VimwikiSearch` keep a
 Vimwiki-only name (shown as `—` in the Nuwiki column); every other
-command is mirrored. The split / tab link-following commands exist on
-the Neovim path only — plain Vim uses the `<S-CR>` / `<C-CR>` mappings
-instead.
+command is mirrored. The split / tab link-following commands are
+available on both the Neovim and plain-Vim paths.
 
 **Wiki & navigation**
 
@@ -379,8 +378,9 @@ instead.
 | `:NuwikiUISelect` | `:VimwikiUISelect` | Pick a wiki from a list (multi-wiki) |
 | `:NuwikiGoto {page}` | `:VimwikiGoto {page}` | Open `{page}.wiki` by name |
 | `:NuwikiFollowLink` | `:VimwikiFollowLink` | Follow the link under the cursor |
-| `:NuwikiSplitLink` / `:NuwikiVSplitLink` / `:NuwikiTabnewLink` | `:VimwikiSplitLink` / `:VimwikiVSplitLink` / `:VimwikiTabnewLink` | Follow the link in a horizontal split / vertical split / new tab (Neovim) |
-| `:NuwikiGoBackLink` | `:VimwikiGoBackLink` | Jump back to where you followed the link from (Neovim) |
+| `:NuwikiSplitLink` / `:NuwikiVSplitLink` / `:NuwikiTabnewLink` | `:VimwikiSplitLink` / `:VimwikiVSplitLink` / `:VimwikiTabnewLink` | Follow the link in a horizontal split / vertical split / new tab |
+| `:NuwikiTabDropLink` | `:VimwikiTabDropLink` | Follow the link in a tab, reusing an existing tab if the file is already open |
+| `:NuwikiGoBackLink` | `:VimwikiGoBackLink` | Jump back to where you followed the link from |
 | `:NuwikiBacklinks` | `:VimwikiBacklinks` (`:VWB`) | Show all references to the current page |
 | `:NuwikiNextLink` / `:NuwikiPrevLink` | `:VimwikiNextLink` / `:VimwikiPrevLink` | Jump to the next / previous wikilink |
 | `:NuwikiBaddLink` | `:VimwikiBaddLink` | Add the link target under the cursor to the buffer list |
@@ -465,7 +465,7 @@ via `mappings.<group> = false` in Neovim, or
 | `<CR>` | Smart follow — inside `[[…]]` jumps; on a bare word wraps as `[[word]]` (second `<CR>` follows) |
 | `<S-CR>` | Follow in horizontal split |
 | `<C-CR>` | Follow in 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>` / `<S-Tab>` | Next / previous wikilink on or after the cursor |
 | `+` | Wrap word / visual selection as a wikilink (no follow) |