fix(buffer): replace indentexpr with dedicated o/O mappings

Problem: setup_indentexpr always returned 0 because no task line
starts with whitespace (the /ID/ prefix begins with /), so the
return 2 branch was dead code. Pressing o or O opened a blank line
at column 0 with no ID prefix, which the diff parser cannot
recognise as a task.

Solution: remove setup_indentexpr and M.get_indent() entirely; add
M.open_line(above) which inserts a two-space stub line and enters
insert mode at the end so the user types directly into the new task
body. The diff layer already handles lines matching ^  .+ as new
tasks. Add o and O buffer-local mappings in init.lua.

lua/pending/buffer.lua

@@ -63,22 +63,19 @@ local function setup_syntax(bufnr)
   end)
 end
 
----@param bufnr integer
-local function setup_indentexpr(bufnr)
-  vim.bo[bufnr].indentexpr = 'v:lua.require("pending.buffer").get_indent()'
-end
 
----@return integer
+---@param above boolean
-function M.get_indent()
+function M.open_line(above)
-  local lnum = vim.v.lnum
+  local bufnr = task_bufnr
-  if lnum <= 1 then
+  if not bufnr or not vim.api.nvim_buf_is_valid(bufnr) then
-    return 0
+    return
   end
-  local prev = vim.fn.getline(lnum - 1)
+  local row = vim.api.nvim_win_get_cursor(0)[1]
-  if prev == '' or prev:match('^%S') then
+  local insert_row = above and (row - 1) or row
-    return 0
+  vim.bo[bufnr].modifiable = true
-  end
+  vim.api.nvim_buf_set_lines(bufnr, insert_row, insert_row, false, { '  ' })
-  return 2
+  vim.api.nvim_win_set_cursor(0, { insert_row + 1, 2 })
+  vim.cmd('startinsert!')
 end
 
 ---@return string
@@ -222,7 +219,6 @@ function M.open()
   vim.api.nvim_buf_set_name(task_bufnr, 'pending://')
 
   set_buf_options(task_bufnr)
-  setup_indentexpr(task_bufnr)
   vim.api.nvim_set_current_buf(task_bufnr)
   set_win_options(vim.api.nvim_get_current_win())
 

lua/pending/init.lua

@@ -61,6 +61,12 @@ function M._setup_buf_mappings(bufnr)
   vim.keymap.set('n', 'U', function()
     M.undo_write()
   end, opts)
+  vim.keymap.set('n', 'o', function()
+    buffer.open_line(false)
+  end, opts)
+  vim.keymap.set('n', 'O', function()
+    buffer.open_line(true)
+  end, opts)
 end
 
 ---@param bufnr integer