dsh-sidebar-mode: Move Agent preset switch into the 'New Session' button

dsh-sidebar-mode is a DSH Desktop profile plugin developed by Meredith2328, designed to optimize the Agent preset switching experience. This plugin integrates the preset selection function into the "New Session" button, allowing users to quickly switch between presets such as Standard and PTC by clicking the tab on the left side of the button without needing to enter the settings panel. Its core functions include: automatically discovering and displaying custom presets; synchronously updating global defaults, the settings panel, and sidebar status during switching; only affecting the current blank session without interfering with running tasks; supporting day/night theme adaptation; and automatically truncating display for long names. Installation requires importing via `pnpm add` and registering it in the `dsh.profile.bundles` field of `package.json`, followed by a restart. This plugin depends on `co`.