- render_files_and_media now wraps the per-file loop in directory groups
via aggregate.group_files_by_dir + imscope.tree_node_ex (mirrors the
Context Composition visual style at gui_2.py:3114)
- New 'Add Directory' button next to 'Add Files to Inventory':
uses filedialog.askdirectory() + os.walk to bulk-import a folder tree
- Button IDs (i, add_f_{i}, rem_f_{i}) preserve global uniqueness via
file_indices map (regression-safe across the directory wrap)
- Test uses mock button=False, mock filedialog.askopenfilenames/askdirectory
to avoid opening a real Tk dialog during test run
