Add togglePlugin() function and IPC command to toggle plugin visibility,
particularly for slideout-capable daemon plugins like AI Assistant.
Implementation uses lazy instantiation for daemon plugins:
- Daemons remain uninstantiated on load (respecting lifecycle)
- First toggle() call instantiates the daemon on-demand
- Subsequent toggles use the existing instance
- Prevents duplicate instantiation while supporting toggle functionality
This approach preserves the fix from f9b9d986 (ensure daemon plugins
not instantiated twice) while enabling new toggle capabilities.
Changes:
- Add PluginService.togglePlugin() with lazy instantiation
- Add DMSShellIPC plugin.toggle() command
- Maintains compatibility with existing daemon plugins
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