Security: Upgrade to PHP 8.x (7.4 is EOL) and ensure CI compatibility

[lucifer4330k]

The Dockerfile uses php:7.4.33-apache, but PHP 7.4 reached end-of-life in Nov 2022 and no longer receives security fixes.

Why this matters

• Security: No upstream patches for CVEs.
• Ecosystem: Many libs drop 7.4 support.

Proposed plan

1. Bump base image to php:8.2-apache (or 8.3).
2. Run the app and fix PHP 8 compatibility issues (CI3 uses some deprecated behaviors).
3. Run unit/integration tests (if available).
4. Update docs re: minimum PHP version.

Acceptance criteria

• Server builds and runs on PHP 8.2+.
• Smoke test of API endpoints passes (data upload/download, runs, flows).
• No fatal errors in logs.

References

• docker/Dockerfile currently pins PHP 7.4.

[agarwalavantika]

Hi @lucifer4330k I'd love to work on this issue. Can you assign me?