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.

tests/test_ui_summary_only_removal.py

@@ -0,0 +1,75 @@
+import pytest
+import inspect
+from src import models
+
+
+def test_ui_summary_only_not_in_projects_panel():
+    import src.gui_2 as gui_2
+
+    source = inspect.getsource(gui_2.App._render_projects_panel)
+    assert "ui_summary_only" not in source, (
+        "ui_summary_only checkbox should be removed from Projects panel"
+    )
+    assert "Summary Only" not in source, (
+        "Summary Only label should be removed from Projects panel"
+    )
+
+
+def test_ui_summary_only_not_in_app_controller_projects():
+    import src.app_controller as app_controller
+
+    source = inspect.getsource(app_controller.AppController)
+    assert "ui_summary_only" not in source, (
+        "ui_summary_only should be removed from AppController"
+    )
+
+
+def test_file_item_has_per_file_flags():
+    item = models.FileItem(path="test.py")
+    assert hasattr(item, "auto_aggregate")
+    assert hasattr(item, "force_full")
+    assert item.auto_aggregate is True
+    assert item.force_full is False
+
+
+def test_file_item_serialization_with_flags():
+    item = models.FileItem(path="test.py", auto_aggregate=False, force_full=True)
+    data = item.to_dict()
+
+    assert data["auto_aggregate"] is False
+    assert data["force_full"] is True
+
+    restored = models.FileItem.from_dict(data)
+    assert restored.auto_aggregate is False
+    assert restored.force_full is True
+
+
+def test_project_without_summary_only_loads():
+    proj = {"project": {"name": "test", "paths": []}}
+    assert proj.get("project", {}).get("summary_only") is None
+
+
+def test_aggregate_from_items_respects_auto_aggregate():
+    from pathlib import Path
+    from src import aggregate
+
+    items = [
+        {
+            "path": Path("file1.py"),
+            "entry": "file1.py",
+            "content": "print('hello')",
+            "auto_aggregate": True,
+            "force_full": False,
+        },
+        {
+            "path": Path("file2.py"),
+            "entry": "file2.py",
+            "content": "print('world')",
+            "auto_aggregate": False,
+            "force_full": False,
+        },
+    ]
+
+    result = aggregate._build_files_section_from_items(items)
+    assert "file1.py" in result
+    assert "file2.py" not in result