feat(PBI-76): user-settings bridge mounted in app layout

Hydrates the zustand store with the user's persisted settings via
prop (SSR-correct, no flicker). Opens an EventSource to
/api/realtime/user-settings so changes from other tabs/devices
flow into the same store. Demo accounts skip the SSE subscription.

Layout now selects user.settings alongside the other user fields,
no extra DB roundtrip.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

components/shared/user-settings-bridge.tsx

@@ -0,0 +1,41 @@
+'use client'
+
+import { useEffect } from 'react'
+import { useUserSettingsStore } from '@/stores/user-settings/store'
+import type { UserSettings } from '@/lib/user-settings'
+
+interface Props {
+  initial: UserSettings
+  isDemo: boolean
+}
+
+/**
+ * PBI-76: hydrates the user-settings Zustand store with server-rendered prefs
+ * and opens an SSE subscription so other tabs/devices of the same user
+ * immediately see changes. Demo accounts skip the SSE subscription — their
+ * settings live only in-memory.
+ */
+export function UserSettingsBridge({ initial, isDemo }: Props) {
+  const hydrate = useUserSettingsStore((s) => s.hydrate)
+  const applyServerPatch = useUserSettingsStore((s) => s.applyServerPatch)
+
+  useEffect(() => {
+    hydrate(initial, isDemo)
+  }, [hydrate, initial, isDemo])
+
+  useEffect(() => {
+    if (isDemo) return
+    const es = new EventSource('/api/realtime/user-settings')
+    es.onmessage = (e) => {
+      try {
+        const patch = JSON.parse(e.data) as Partial<UserSettings>
+        applyServerPatch(patch)
+      } catch {
+        // ignore malformed event
+      }
+    }
+    return () => es.close()
+  }, [applyServerPatch, isDemo])
+
+  return null
+}