docs: update README with tech stack summary, cleaner prerequisites, and contributing section

[devin-ai-integration]

Summary

Minor README improvements:

• Added key technologies (React, Node.js, Express, SQLite) to the opening description
• Simplified prerequisites section (removed yarn reference, clarified npm comes with Node.js)
• Replaced the generic "Support" section with a "Contributing" section
• Removed redundant support contact line

Review & Testing Checklist for Human

• Verify the README renders correctly on GitHub

Notes

Documentation-only change — no code or tests affected.

Link to Devin session: https://partner-workshops.devinenterprise.com/sessions/8d7581fa7d5d4162a8105d90269e978b
Requested by: @bsmitches

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[devin-ai-integration]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.