Replace PrimeVue Divider with design-system primitives

## Background

As part of the ongoing migration away from PrimeVue components to shadcn/vue and Reka UI, we should replace all usages of the PrimeVue `Divider` component with design-system-backed separators.

## Context

This was identified during review of PR #7223:
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7223#discussion_r2608871632

## Current Usage

The `Divider` component from PrimeVue is currently used in **22 files** across the codebase:

### Main App
- `src/views/UserSelectView.vue`
- `src/platform/settings/components/SettingGroup.vue`
- `src/platform/settings/components/ServerConfigPanel.vue`
- `src/platform/settings/components/SettingDialogContent.vue`
- `src/platform/cloud/onboarding/CloudSignupView.vue`
- `src/platform/cloud/onboarding/CloudLoginView.vue`
- `src/components/topbar/CurrentUserPopover.vue`
- `src/components/sidebar/tabs/ModelLibrarySidebarTab.vue`
- `src/components/sidebar/tabs/AssetsSidebarTab.vue`
- `src/components/sidebar/tabs/NodeLibrarySidebarTab.vue`
- `src/components/dialog/content/SignInContent.vue`
- `src/components/dialog/content/setting/UserPanel.vue`
- `src/components/dialog/content/setting/LegacyCreditsPanel.vue`
- `src/components/dialog/content/setting/AboutPanel.vue`
- `src/components/dialog/content/ErrorDialogContent.vue`
- `src/components/common/TextDivider.vue`
- `src/components/common/SystemStatsPanel.vue`
- `src/components/common/CustomizationDialog.vue`

### Desktop App
- `apps/desktop-ui/src/components/maintenance/TaskListPanel.vue`
- `apps/desktop-ui/src/components/install/InstallLocationPicker.vue`
- `apps/desktop-ui/src/components/install/mirror/MirrorItem.vue`
- `apps/desktop-ui/src/components/install/DesktopSettingsConfiguration.vue`

## Proposed Solution

Replace PrimeVue `Divider` with one of:
1. Enhanced `TextDivider` component (which itself wraps PrimeVue Divider currently, so would need updating)
2. Simple Tailwind-based dividers using theme tokens from `style.css` (e.g., `