feat: DashboardShell for all auth pages, site settings modal from home

- layout-content wraps integrations/pricing in DashboardShell
- GlassTopBar derives title per page (Integrations, Pricing, etc.)
- Site card gear icon opens settings modal with siteId context
- Removed delete button from site cards (accessible via site settings)
- Extended InitialTab to accept optional siteId for cross-page use

lib/unified-settings-context.tsx

@@ -2,7 +2,7 @@
 
 import { createContext, useContext, useState, useCallback } from 'react'
 
-type InitialTab = { context?: 'site' | 'workspace' | 'account'; tab?: string } | null
+type InitialTab = { context?: 'site' | 'workspace' | 'account'; tab?: string; siteId?: string } | null
 
 interface UnifiedSettingsContextType {
   isOpen: boolean