refactor(buffer): remove opinionated window options, fix close (#32)

* fix(plugin): allow command chaining with bar separator

Problem: :Pending|only failed because the command definition lacked the
bar attribute, causing | to be consumed as an argument.

Solution: Add bar = true to nvim_create_user_command so | is treated as
a command separator, matching fugitive's :Git behavior.

* refactor(buffer): remove opinionated window options

Problem: The plugin hardcoded number, relativenumber, wrap, spell,
signcolumn, foldcolumn, and cursorline in set_win_options, overriding
user preferences with no way to opt out.

Solution: Remove all cosmetic window options. Users who want them can
set them in after/ftplugin/pending.lua. Only conceallevel,
concealcursor, and winfixheight remain as functionally required.

lua/pending/buffer.lua

@@ -69,13 +69,6 @@ end
 local function set_win_options(winid)
   vim.wo[winid].conceallevel = 3
   vim.wo[winid].concealcursor = 'nvic'
-  vim.wo[winid].wrap = false
-  vim.wo[winid].number = false
-  vim.wo[winid].relativenumber = false
-  vim.wo[winid].signcolumn = 'no'
-  vim.wo[winid].foldcolumn = '0'
-  vim.wo[winid].spell = false
-  vim.wo[winid].cursorline = true
   vim.wo[winid].winfixheight = true
 end