Add CodeMash conference data

[artrmkr]

/claim #10

Summary

• Add CodeMash to the conference dataset.
• Preserve the existing README table schema.
• Use conservative SEA value because no public commitment to sign the Speaker Engagement Agreement was found.

Source notes

• CodeMash official site: https://codemash.org/
• CodeMash organizer page identifies the volunteer organizer team: https://codemash.org/organizers/
• CodeMash speaker benefits list a four-day pass, hotel/housing credit, and a $250 PreCompiler workshop honorarium: https://codemash.org/call-for-speakers-announcement/

Verification

• python3 README table check: 12 conference rows, all with 6 columns.
• git diff --check
• Source link check: 3 CodeMash 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 #334 for #10.

It adds CodeMash with public organizer and speaker-benefit sources, preserves the README table schema, includes /claim #10, 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!