Fix GitHub Pages deploy: add package-lock.json + fix React version

[txmed82]

Problem\nThe Docusaurus deploy workflow failed because:\n1. No existed in , so could not resolve/cache dependencies.\n2. does not exist on npm, causing to fail entirely.\n\n## Fix\n- Downgrade and from to (Docusaurus 3.8.1 compatible).\n- Add generated so works in CI.\n\n## After merge\nThe workflow should succeed and the site should appear at https://txmed82.github.io/retrace/

Summary by CodeRabbit

• Chores
  • Updated React framework dependencies to enhance platform stability and maintain compatibility across the application.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 33e3ae21-3c7f-4939-a329-83ba664fd9a5

📥 Commits

Reviewing files that changed from the base of the PR and between 4fdcfb8 and cfaf3e2.

⛔ Files ignored due to path filters (1)

• website/package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (1)

• website/package.json

---

📝 Walkthrough

Walkthrough

The website package.json downgrades React and React DOM from version 19.3.1 to version 18.3.1, shifting the runtime dependency constraints from the React 19 major version range to React 18.

Changes

React Version Downgrade

Layer / File(s)	Summary
React version downgrade website/package.json	react and react-dom dependencies are downgraded from ^19.3.1 to ^18.3.1.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

A hop and a skip, the version descends,
From React's newest dawn, back to steadier ends.
Version 18 awaits with open paws,
Down from 19's height—trust the downgrade clause! 🐰

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main changes: downgrading React version and adding package-lock.json to fix GitHub Pages deployment issues.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-pages-deploy

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}