fix(buffer): reveal concealed text on cursor line in insert mode (#166)

Problem: `concealcursor` was set to `'nic'`, keeping forge tokens and
task IDs concealed even in insert mode. This makes editing lines with
`gh:user/repo#42` or full URLs difficult since the raw text is hidden.

Solution: Change `concealcursor` from `'nic'` to `'nc'` so the cursor
line reveals concealed text when entering insert mode.

lua/pending/buffer.lua

@@ -399,7 +399,7 @@ end
 ---@param winid integer
 local function set_win_options(winid)
   vim.wo[winid].conceallevel = 3
-  vim.wo[winid].concealcursor = 'nic'
+  vim.wo[winid].concealcursor = 'nc'
   vim.wo[winid].winfixheight = true
 end