Restore CI and release workflows

[yvette-carlisle]

Summary

• restore GitHub Actions for language checks, Pages deployment, and tagged releases
• restore Dependabot for Cargo, GitHub Actions, and the site npm workspace
• remove the checked-in CodeQL workflow and remove workflow path filtering
• adapt release packaging to the current Decodex.app bundle identity
• keep Radar and release-curation automations in Codex App rather than GitHub Actions

Validation

• cargo make check
• actionlint
• Ruby YAML parse for all checked-in workflows
• scripts/macos/test_decodex_app_stage.sh
• openwiki code --update --print (reviewed; unrelated generated automation was discarded)
• git diff --check