feat(seo): add URL lang param, dynamic hreflang alternates, and multilingual sitemap

[gzz727007]

🦭 Pull Request Description

Summary of Changes

1. URL Language Query Parameter & Synchronization (src/i18n.js):

   • Added top-priority URL query parameter parsing (?lang=ja or ?hl=ja) in getInitialLang(), enabling search engine crawlers and users to bookmark or share direct localized links.
   • Automatically synchronizes active language changes to the URL via window.history.replaceState without triggering page reload.
   • Cleans up query parameter when switching back to default English, keeping clean canonical URLs.

2. Dynamic hreflang Alternates & Canonical URLs (src/utils/seo.js):

   • Injects Google and Bing compliant <link rel="alternate" hreflang="..."> tags for all 6 supported languages (en, de, es, fr, ja, zh, zh-Hans, and x-default).
   • Ensures self-referential canonical links and Open Graph (og:url) tags dynamically match the active localized page URL.

3. Multilingual sitemap.xml Generator (vite.config.js):

   • Upgraded sitemap generation with the standard xmlns:xhtml="http://www.w3.org/1999/xhtml" specification.
   • Generates 102 indexed multilingual URLs covering all 17 routes (homepage + 16 utilities) with reciprocal xhtml:link alternate annotations and priority weights.

4. Version Bump & Test Suite Alignment:

   • Bumped version to 1.2.2 across package.json, package-lock.json, and siteConfig.js.
   • Updated test suite origins in tests/routerSeo.test.js and tests/pdfToImage.test.js to match the official site https://pdf.sealkit.org.
   • Added unit test cases for URL language parameter detection and hreflang tag generation (all 36 test suites, 230 tests passing 100%).
   • Updated documentation in README.md and README.zh-CN.md using standard native endonyms terminology.

Type of Change

• 🐛 Bug fix (non-breaking change fixing an issue)
• ✨ New feature (non-breaking change adding functionality)
• ⚡ Performance optimization (rendering, memory, or bundle size)
• 🎨 UI / UX refinement
• 🌍 Internationalization / Translations (new or updated language)
• 📝 Documentation update (README, Guides, Comments)
• 🧪 Test suite enhancement

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🛡️ Privacy & Quality Checklist

• 100% Client-Side Invariant: All code runs strictly in the browser RAM / WebAssembly. No user documents or telemetry data are ever sent over the network.
• Automated Tests: I have verified that all existing tests pass (npm test -> 36 suites, 230 tests passing 100%).
• New Tests Added: Added hreflang and URL search parameter tests in tests/routerSeo.test.js.
• Responsive & Cross-Browser: Verified that UI works smoothly across desktop and mobile screens.
• Self-Review: I have performed a self-review of my own code and removed unnecessary console.log statements.

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Related Issues

Closes #

[cloudflare-workers-and-pages]

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	pdfseal	5317072	Commit Preview URL Branch Preview URL	Sep 25 2026, 08:04 AM