perf: deduplicate common namespace serialization across layout and page providers

[pettinarip]

Summary

• Eliminate double-serialization of the common i18n namespace in HTML payload
• Layout provider serializes "common" once; page providers now merge parent messages instead of replacing them
• No changes needed to any of the 29 page files — the merge happens automatically in I18nProvider

Problem

The common namespace (~26KB) was serialized twice on every page:

1. Layout-level NextIntlClientProvider in providers.tsx serialized it for layout components
2. Page-level I18nProvider also included it via getRequiredNamespacesForPage()

Per next-intl behavior, nested providers treat messages as atomic replacements — the page provider's messages completely replaced the layout's. This forced pages to re-include "common".

Solution (3 files)

1. providers.tsx — Use NextIntlClientProvider directly as root provider (no merging needed)
2. I18nProvider.tsx — Call useMessages() to get parent provider's messages and merge with page-specific messages on the client
3. translations.ts — Remove "common" from getRequiredNamespacesForPage() base namespaces

How it works

Layout: serializes { common: {...} } once → NextIntlClientProvider
  └── Page: serializes only { "page-wallets": {...} } → I18nProvider
        ├── useMessages() returns { common: {...} } from parent
        ├── merged = { common: {...}, "page-wallets": {...} }
        └── NextIntlClientProvider gets merged messages

Test plan

• TypeScript type check passes (pnpm tsc --noEmit)
• Production build succeeds (pnpm build)
• Desktop nav: click through all 5 sections, verify labels render
• Mobile nav: open hamburger menu, verify labels, theme toggle, search
• Search modal: verify all UI strings on desktop and mobile
• FeedbackWidget: click floating dot, verify prompt and yes/no buttons
• RTL locale (e.g. /ar/): verify nav direction and layout
• HTML payload: verify "common" namespace appears only once

[github-actions]

This issue is stale because it has been open 30 days with no activity.