added a flag to hide settings (#5263)

Added an optional flag in settings.yml to hide the settings button in no
login servers. When hidden, users can no longer:

- Open the Settings modal at all (gear button is hidden)
- Change General preferences (tool picker mode, hide unavailable
tools/conversions, auto‑unzip and file limit)
- Configure keyboard shortcuts (Hotkeys / Keyboard Shortcuts section)
- Use the in‑app update checker UI (see current/latest version, check
for updates, view update details)
- Note: When enableLogin === true, the flag is ignored and the Settings
button remains visible.

---------

Co-authored-by: Anthony Stirling <[email protected]>
Co-authored-by: Reece Browne <[email protected]>

frontend/src/core/contexts/AppConfigContext.tsx

@@ -23,6 +23,7 @@ export interface AppConfig {
   defaultLocale?: string;
   logoStyle?: 'modern' | 'classic';
   enableLogin?: boolean;
+  showSettingsWhenNoLogin?: boolean;
   enableEmailInvites?: boolean;
   isAdmin?: boolean;
   enableAlphaFunctionality?: boolean;