feat(buffer): re-apply inline extmarks after edits

Problem: inline extmarks (checkbox overlays, strikethrough, header
highlights) were cleared during edits and only restored on `:w`,
leaving the buffer visually bare while editing.

Solution: extract `apply_inline_row()` from `apply_extmarks()` and
call it via `reapply_dirty_inline()` on `InsertLeave` and normal-mode
`TextChanged`. Insert-mode `TextChangedI` still only clears inline
marks on dirty rows to avoid overlay flicker while typing.

lua/pending/init.lua

@@ -251,7 +251,7 @@ function M._setup_autocmds(bufnr)
       end
     end,
   })
-  vim.api.nvim_create_autocmd({ 'TextChanged', 'TextChangedI' }, {
+  vim.api.nvim_create_autocmd('TextChangedI', {
     group = group,
     buffer = bufnr,
     callback = function()
@@ -263,6 +263,25 @@ function M._setup_autocmds(bufnr)
       end
     end,
   })
+  vim.api.nvim_create_autocmd('TextChanged', {
+    group = group,
+    buffer = bufnr,
+    callback = function()
+      if not vim.bo[bufnr].modified then
+        return
+      end
+      buffer.reapply_dirty_inline(bufnr)
+    end,
+  })
+  vim.api.nvim_create_autocmd('InsertLeave', {
+    group = group,
+    buffer = bufnr,
+    callback = function()
+      if vim.bo[bufnr].modified then
+        buffer.reapply_dirty_inline(bufnr)
+      end
+    end,
+  })
   vim.api.nvim_create_autocmd('WinClosed', {
     group = group,
     callback = function(ev)