fix(ui): guard against non-functional localStorage in Node/SSR environment (fixes #5379)

[asheesh-devops]

Summary

Fixes TypeError: localStorage.getItem is not a function that crashes the /signin page with a 500 error on first run of docker compose -f docker-compose.dev.yml up.

Root Cause

When Node.js is started with the --localstorage-file flag without a valid path (as happens in the Docker dev setup), the global localStorage object exists but getItem/setItem are not proper functions. The existing guard in useLocalStorage hook only checks typeof localStorage === "undefined" which passes, leading to:

TypeError: localStorage.getItem is not a function
⨯ [TypeError: localStorage.getItem is not a function] { page: '/signin' }

The Fix

Add additional type checks for getItem/setItem being actual functions:

// Before (broken):
if (typeof window === "undefined" || typeof localStorage === "undefined") {
  return null;
}
return localStorage.getItem(`keephq-${key}`);  // FAILS - getItem is not a function

// After (fixed):
if (
  typeof window === "undefined" ||
  typeof localStorage === "undefined" ||
  typeof localStorage.getItem !== "function"
) {
  return null;  // Gracefully falls back
}
return localStorage.getItem(`keephq-${key}`);  // Works!

Changes

• keep-ui/utils/hooks/useLocalStorage.ts — enhanced SSR guards in getSnapshot() and setLocalStorageValue()

Testing

• Verified this is the central useLocalStorage hook used by 26+ components across the app
• The useSyncExternalStore third argument (server snapshot) returns JSON.stringify(initialValue) so the hook gracefully degrades during SSR
• Confirmed no other direct localStorage calls in the signin page flow — all go through this hook

Fixes #5379