fix(nvim): keep window layout when closing a buffer

`:bdelete` closes the window when no other listed buffer is left for it to
show, so closing the last file with neo-tree open left a full-width tree.
Point the window at another listed buffer, or a fresh empty one, before
deleting. `confirm` matches `<leader>Q`, prompting instead of failing on a
modified buffer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015D4NsszUG7hy9ghKZ4nfhm

modules/nvim.nix

@@ -285,7 +285,26 @@ in
         # Buffer navigation (no bufferline: cycle with Shift-h/l, list via <leader>fb)
         { mode = "n"; key = "<S-l>"; action = "<cmd>bnext<cr>"; options.desc = "Next buffer"; }
         { mode = "n"; key = "<S-h>"; action = "<cmd>bprevious<cr>"; options.desc = "Prev buffer"; }
-        { mode = "n"; key = "<leader>bd"; action = "<cmd>bdelete<cr>"; options.desc = "Close buffer"; }
+        # Plain `:bdelete` closes the window when no other listed buffer is left
+        # for it to show, which with neo-tree open leaves a full-width tree.
+        # Point the window at another buffer (or a fresh empty one) first, so the
+        # layout survives; `confirm` prompts rather than failing when modified.
+        {
+          mode = "n";
+          key = "<leader>bd";
+          action.__raw = ''
+            function()
+              local cur = vim.api.nvim_get_current_buf()
+              local listed = vim.tbl_filter(
+                function(b) return vim.bo[b].buflisted end,
+                vim.api.nvim_list_bufs()
+              )
+              if #listed > 1 then vim.cmd('bprevious') else vim.cmd('enew') end
+              vim.cmd('confirm bdelete ' .. cur)
+            end
+          '';
+          options.desc = "Close buffer";
+        }
 
         # Terminal: toggle a horizontal or vertical split (toggleterm). Same key
         # hides it again. From inside the terminal, <C-w> drops to normal mode and