refactor: remove dead main_context field from Project Settings

The main_context field in Project Settings was stored but never used.
Nothing reads it to inject into AI context. System Prompt in AI Settings
already serves this purpose.

Removed:
- app_controller.py: ui_project_main_context state variable and all refs
- gui_2.py: Main Context File UI section from Projects panel
- project_manager.py: main_context from default_project()
- project.toml, manual_slop.toml, gencpp_manual_slop_template.toml: main_context entries

src/app_controller.py

@@ -254,7 +254,6 @@ class AppController:
   self.ui_files_base_dir: str = ""
   self.ui_shots_base_dir: str = ""
   self.ui_project_git_dir: str = ""
-  self.ui_project_main_context: str = ""
   self.ui_project_system_prompt: str = ""
   self.ui_project_execution_mode: str = "native"
   self.ui_gemini_cli_path: str = "gemini"
@@ -367,7 +366,6 @@ class AppController:
    'project_git_dir': 'ui_project_git_dir',
    'auto_add_history': 'ui_auto_add_history',
    'disc_new_name_input': 'ui_disc_new_name_input',
-   'project_main_context': 'ui_project_main_context',
    'gcli_path': 'ui_gemini_cli_path',
    'output_dir': 'ui_output_dir',
    'files_base_dir': 'ui_files_base_dir',
@@ -1186,7 +1184,6 @@ class AppController:
   proj_meta = self.project.get("project", {})
   self.ui_project_git_dir = proj_meta.get("git_dir", "")
   self.ui_project_conductor_dir = self.project.get('conductor', {}).get('dir', 'conductor')
-  self.ui_project_main_context = proj_meta.get("main_context", "")
   self.ui_project_system_prompt = proj_meta.get("system_prompt", "")
   self.ui_gemini_cli_path = self.project.get("gemini_cli", {}).get("binary_path", "gemini")
   self._update_gcli_adapter(self.ui_gemini_cli_path)
@@ -2381,7 +2378,6 @@ class AppController:
   proj_meta = self.project.get("project", {})
   self.ui_project_git_dir = proj_meta.get("git_dir", "")
   self.ui_project_system_prompt = proj_meta.get("system_prompt", "")
-  self.ui_project_main_context = proj_meta.get("main_context", "")
   self.ui_project_preset_name = proj_meta.get("active_preset")
   self.ui_gemini_cli_path = self.project.get("gemini_cli", {}).get("binary_path", "gemini")
   self.ui_auto_add_history = proj.get("discussion", {}).get("auto_add", False)
@@ -2812,7 +2808,6 @@ class AppController:
   self.ui_global_system_prompt = ''
   self.ui_base_system_prompt = ''
   self.ui_project_system_prompt = ''
-  self.ui_project_main_context = ''
   self.ui_active_persona = ''
   self.ui_active_tool_preset = None
   self.ui_active_bias_profile = None
@@ -2982,7 +2977,6 @@ class AppController:
   proj["project"]["git_dir"] = self.ui_project_git_dir
   proj.setdefault("conductor", {})["dir"] = self.ui_project_conductor_dir
   proj["project"]["system_prompt"] = self.ui_project_system_prompt
-  proj["project"]["main_context"] = self.ui_project_main_context
   proj["project"]["active_preset"] = self.ui_project_preset_name
   proj["project"]["word_wrap"] = self.ui_word_wrap
   proj["project"]["auto_scroll_comms"] = self.ui_auto_scroll_comms