feat(settings): unified settings modal with context switcher (Phase 1)

New unified settings modal accessible via `,` keyboard shortcut.
Three-context switcher: Site (with site dropdown), Workspace, Account.
Horizontal tabs per context with animated transitions.

Phase 1 tabs implemented:
- Site → General (name, timezone, domain, tracking script with copy)
- Site → Goals (CRUD with inline create/edit)
- Workspace → General (org name, slug, danger zone)
- Workspace → Billing (plan card, usage, cancel/resume, portal)
- Account → Profile (wraps existing ProfileSettings)

Phase 2 tabs show "Coming soon" placeholder:
- Site: Visibility, Privacy, Bot & Spam, Reports, Integrations
- Workspace: Members, Notifications, Audit Log
- Account: Security, Devices

Old settings pages and profile modal remain functional.

lib/unified-settings-context.tsx

@@ -0,0 +1,44 @@
+'use client'
+
+import { createContext, useContext, useState, useCallback } from 'react'
+
+type InitialTab = { context?: 'site' | 'workspace' | 'account'; tab?: string } | null
+
+interface UnifiedSettingsContextType {
+  isOpen: boolean
+  openUnifiedSettings: (initialTab?: InitialTab) => void
+  closeUnifiedSettings: () => void
+  initialTab: InitialTab
+}
+
+const UnifiedSettingsContext = createContext<UnifiedSettingsContextType>({
+  isOpen: false,
+  openUnifiedSettings: () => {},
+  closeUnifiedSettings: () => {},
+  initialTab: null,
+})
+
+export function UnifiedSettingsProvider({ children }: { children: React.ReactNode }) {
+  const [isOpen, setIsOpen] = useState(false)
+  const [initialTab, setInitialTab] = useState<InitialTab>(null)
+
+  const openUnifiedSettings = useCallback((init?: InitialTab) => {
+    setInitialTab(init || null)
+    setIsOpen(true)
+  }, [])
+
+  const closeUnifiedSettings = useCallback(() => {
+    setIsOpen(false)
+    setInitialTab(null)
+  }, [])
+
+  return (
+    <UnifiedSettingsContext.Provider value={{ isOpen, openUnifiedSettings, closeUnifiedSettings, initialTab }}>
+      {children}
+    </UnifiedSettingsContext.Provider>
+  )
+}
+
+export function useUnifiedSettings() {
+  return useContext(UnifiedSettingsContext)
+}