fix(project): Reload context_files from new project on project switch

When switching projects, the previous project's context_files remained
visible in the Context Composition panel because the controller's
self.context_files list was not reloaded from the new project's TOML
files.paths entry.

Fix in _refresh_from_project:
- After loading self.files from the project TOML, populate
  self.context_files with deep copies of those FileItem objects
- Reset self._app.ui_selected_context_files to match the new project's
  auto_aggregate set
- Guard the _app access with hasattr so the controller is usable
  standalone (in tests, headless mode, etc.) without an attached App

Test: 1 new test in tests/test_project_switch_persona_preset.py
- test_switch_project_resets_context_files: switches from project_a
  (forth + gte_hello files) to project_b (gencpp timing files) and
  asserts context_files contains ONLY project_b's files

tests/test_project_switch_persona_preset.py

@@ -170,3 +170,51 @@ def test_load_context_preset_missing_raises_keyerror(tmp_path, monkeypatch):
 
     with pytest.raises(KeyError, match="Context preset 'NonexistentPreset' not found"):
         ctrl.load_context_preset("NonexistentPreset")
+
+
+def test_switch_project_resets_context_files(tmp_path, monkeypatch):
+    project_a_path, project_b_path = _setup_two_projects(tmp_path)
+
+    proj_a_data = '''[project]
+name = "project_a"
+[files]
+base_dir = "."
+paths = [
+  { path = "C:/projects/forth/bootslop/main.c", view_mode = "full" },
+  { path = "C:/projects/Pikuma/ps1/code/gte_hello/hello_gte.c", view_mode = "full" },
+]
+'''
+    project_a_path.write_text(proj_a_data)
+
+    proj_b_data = '''[project]
+name = "project_b"
+[files]
+base_dir = "."
+paths = [
+  { path = "C:/projects/gencpp/base/dependencies/timing.cpp", view_mode = "full" },
+  { path = "C:/projects/gencpp/base/dependencies/timing.hpp", view_mode = "full" },
+]
+'''
+    project_b_path.write_text(proj_b_data)
+
+    ctrl = AppController()
+    monkeypatch.setattr(ctrl, "_rebuild_rag_index", lambda: None)
+    monkeypatch.setattr(ctrl, "_flush_to_project", lambda: None)
+
+    ctrl.active_project_path = str(project_a_path)
+    ctrl.project = project_manager.load_project(str(project_a_path))
+    ctrl.preset_manager = presets.PresetManager(Path(project_a_path).parent)
+    ctrl.tool_preset_manager = tool_presets.ToolPresetManager(Path(project_a_path).parent)
+    ctrl.persona_manager = PersonaManager(Path(project_a_path).parent)
+    ctrl._refresh_from_project()
+
+    assert len(ctrl.context_files) == 2
+    assert any("forth" in f.path for f in ctrl.context_files)
+    assert any("gte_hello" in f.path for f in ctrl.context_files)
+
+    ctrl._switch_project(str(project_b_path))
+
+    assert len(ctrl.context_files) == 2
+    assert all("gencpp" in f.path for f in ctrl.context_files)
+    assert not any("forth" in f.path for f in ctrl.context_files)
+    assert not any("gte_hello" in f.path for f in ctrl.context_files)