fix: improve sitemap generator for better Google Search Console compatibility

[TechGenius-Karan]

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🔍 Description

Improves the sitemap generation script to resolve the Google Search Console
indexing issue (#107):

• Removes unused XML namespaces (news, xhtml, image, video) that were
  declared but never used — these can confuse crawlers
• Adds <lastmod> dates to all URLs (blog, simulation, and static routes)
• Adds explicit <?xml version="1.0" encoding="UTF-8"?> declaration
• Uses path.join() + __dirname for correct cross-platform file paths
• Ensures public/ directory exists before writing (defensive)
• Simplifies out/ directory handling using existsSync (removes dynamic imports)
• Adds process.exit(1) on failure so CI fails visibly if sitemap errors
• Adds summary output for verification

This replicates the approach from PR #290 with Prettier formatting applied.

✅ Checklist

• I have read the CONTRIBUTING.md
• My changes follow the code style of this project
• I ran npm run format — Prettier passes on the changed file
• No new ESLint errors introduced

🎨 Visual Changes

No UI changes — build script only.

📂 Type of Change

• Bug fix

🧩 Additional Notes for Reviewers

This is a re-implementation of PR #290 which the maintainer said would be merged
if prettier errors were fixed. Prettier has been applied and the file passes
npx prettier --check scripts/sitemap-generator.js. The current file also
includes the simulationRoutes (added after #290 was opened), which have been
given lastmod dates as well.

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🎉 This PR is included in version 3.29.0 🎉

The release is available on GitHub release

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