Add Scala Days conference data

[artrmkr]

/claim #4

Summary

• Add Scala Days to the conference dataset.
• Preserve the existing README table schema.
• Use conservative values where no public SEA, reimbursement, or honorarium commitments were found.

Source notes

• Official Scala Days site lists the current conference: https://scaladays.org/
• The Scala language announcement says Scala Center partnered with Plain Schwarz for Scala Days 2026: https://www.scala-lang.org/blog/2026/03/26/scala-days-2026.html
• The current CFP describes talks, labs, and workshops: https://www.scala-lang.org/blog/2026/04/30/scala-days-2026-cfp.html

Verification

• python3 README table check: 12 conference rows, all with 6 columns.
• git diff --check
• Source link check: Scala Days source URLs returned HTTP 200.

Demo note: this is a static README data update, so the PR diff is the review/demo surface.

[artrmkr]

Hi @jdegoes, just following up on PR #333 for #4.

It adds Scala Days with current public sources, preserves the README table schema, includes /claim #4, and includes validation notes for the table column-count check, git diff --check, and HTTP 200 source-link checks.

Happy to adjust anything you want changed before review/reward. Thanks!