Add CodeMash conference data

[CharlieLZ]

/claim #10

Summary

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

Source notes

• CodeMash official site: https://codemash.org/
• CodeMash FAQ identifies CodeMash Conference as an Ohio non-profit and describes the volunteer organization: https://codemash.org/faq/
• CodeMash organizer page lists the volunteer organizer team: https://codemash.org/organizers/
• CodeMash speaker benefits list a four-day pass, hotel/housing credit, and a PreCompiler honorarium: https://codemash.org/call-for-speakers-announcement/

Verification

• rg -n "CodeMash" README.md
• awk README table pipe-count check: all table rows have 6 columns.
• git diff --check
• Source link check with curl -fsSL --connect-timeout 5 --max-time 20 -o /dev/null for all cited source URLs.

Demo

• Static data update demo/validation video: https://github.com/CharlieLZ/conference-data/releases/download/conference-data-350-351-demo/conference-data-350-351-demo.mp4

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