fix(cli): write editor draft to prompt.md so syntax highlighting works

Base CLI was handing prompt_toolkit's Buffer.open_in_editor() a default
config — Buffer.tempfile_suffix and .tempfile both empty — so it
created /tmp/tmpXXXXXX with no extension. nano/vim/helix all key
syntax highlighting off the file extension, so the buffer rendered
plain.

The TUI already writes to <mkdtemp>/prompt.md and gets full markdown
highlighting + a sensible title bar. Set buffer.tempfile = 'prompt.md'
on the TextArea so prompt_toolkit's complex-tempfile path produces
<mkdtemp>/prompt.md to match. shutil.rmtree cleanup is built-in.

cli.py

@@ -9783,6 +9783,12 @@ class HermesCLI:
                 completer=_completer,
             ),
         )
+        # Match the TUI's editor handoff: the temp file lands at
+        # <mkdtemp>/prompt.md so vim/nano/helix pick up markdown syntax
+        # highlighting from the .md extension and the title bar reads
+        # "prompt.md" instead of a random "tmpXXXXXX". prompt_toolkit's
+        # complex-tempfile path takes care of cleanup via shutil.rmtree.
+        input_area.buffer.tempfile = 'prompt.md'
 
         # Dynamic height: accounts for both explicit newlines AND visual
         # wrapping of long lines so the input area always fits its content.