feat(gui): Remove ui_summary_only global toggle

The ui_summary_only global aggregation toggle was redundant with per-file flags
(auto_aggregate, force_full). Removed:
- Checkbox from Projects panel (gui_2.py)
- State variable and project load/save (app_controller.py)

Per-file flags remain the intended mechanism for controlling aggregation.

Tests added to verify removal and per-file flag functionality.

src/gui_2.py

@@ -1702,7 +1702,6 @@ class App:
    models.save_config(self.config)
    self.ai_status = "config saved"
   ch, self.ui_word_wrap = imgui.checkbox("Word-Wrap (Read-only panels)", self.ui_word_wrap)
-  ch, self.ui_summary_only = imgui.checkbox("Summary Only (send file structure, not full content)", self.ui_summary_only)
   ch, self.ui_auto_scroll_comms = imgui.checkbox("Auto-scroll Comms History", self.ui_auto_scroll_comms)
   ch, self.ui_auto_scroll_tool_calls = imgui.checkbox("Auto-scroll Tool History", self.ui_auto_scroll_tool_calls)
   if self.perf_profiling_enabled: self.perf_monitor.end_component("_render_projects_panel")