feat(buffer): clear only inline extmarks on dirty rows during edits

Problem: `TextChanged` cleared all extmarks (both namespaces) on every
edit, causing EOL virtual text (due dates, recurrence) to vanish while
the user types.

Solution: replace blanket `clear_marks()` with per-row
`clear_inline_row()` that only removes `ns_inline` extmarks on rows
flagged dirty by `on_bytes`. EOL virtual text is preserved untouched.

lua/pending/buffer.lua

@@ -99,6 +99,13 @@ function M.clear_marks(b)
   vim.api.nvim_buf_clear_namespace(bufnr, ns_inline, 0, -1)
 end
 
+---@param b integer
+---@param row integer
+---@return nil
+function M.clear_inline_row(b, row)
+  vim.api.nvim_buf_clear_namespace(b, ns_inline, row - 1, row)
+end
+
 ---@return table<integer, true>
 function M.dirty_rows()
   return _dirty_rows

lua/pending/init.lua

@@ -255,8 +255,11 @@ function M._setup_autocmds(bufnr)
     group = group,
     buffer = bufnr,
     callback = function()
-      if vim.bo[bufnr].modified then
-        buffer.clear_marks(bufnr)
+      if not vim.bo[bufnr].modified then
+        return
+      end
+      for row in pairs(buffer.dirty_rows()) do
+        buffer.clear_inline_row(bufnr, row)
       end
     end,
   })