feat: add multi-language (i18n) support to UI (#198)

[spartan124]

PR Description

## Description
This PR implements multi-language (i18n) support across the UI (resolving #198). It introduces a

lightweight, type-safe, locale-aware translation system with fallback support, dynamic client-side
language switching, and automated translation key verification during the lint phase.

## Changes

### 1. Localization Storage & Setup
- Created translation dictionaries under  for `en`, `pt`, and `es`.
- Upgraded the i18n.ts hook to dynamically read from the active language, with variable

interpolation and English fallback.

### 2. User Settings & RTL Layout
- Added a Language selector dropdown to the page.tsx that persists user preference in

localStorage.
- Enabled automatic dir and lang synchronization on document.documentElement inside
SettingsContext.tsx to support RTL layouts (e.g., Arabic/Hebrew) when registering new locales.

### 3. Locale-Aware Formatting
- Integrated locale-aware dates, decimals, and currencies into components such as LiveCounter.tsx (for

ticking balances), NavHeader.tsx (for XLM balances), StreamTimeline.tsx, and StreamHistory.tsx.

### 4. CI Validation & Contribution Documentation
- Created a validation script check-i18n.mjs that fails the lint step if translations are out of sync

with en.json.
- Added translation guidelines to CONTRIBUTING.md to help community members submit translations.

### 5. Code Quality & Prerendering Fixes
- Wrapped the page.tsx in `Suspense` to fix the Next.js CSR search-params prerendering bailout.
- Fixed pre-existing rules of hooks / hoisting errors in WalletContext.tsx and page.tsx.

## Verification Results

### Tests
All **14 test files and 88 unit tests** execute and pass successfully:
```bash
Test Files  14 passed (14)
     Tests  88 passed (88)

Build & Lints

Next.js production compiles successfully and the translation check script completes cleanly:

next lint && node scripts/check-i18n.mjs
All translations are in sync!

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