ci: add validation and release workflow

[ricochet]

This pr adds GH Workflows.

Release Flow:

1. Run Prepare Release workflow
2. Review and merge the generated PR
3. Run Publish Release workflow

CI (ci.yml)

• Validates WIT syntax on push/PR to main

Prepare Release (prepare-release.yml)

• Manual trigger via workflow_dispatch
• Auto-increments RC version (e.g., 0.2.0-rc.1 → 0.2.0-rc.2)
• Creates PR with version bump in wit/world.wit

Publish Release (publish-release.yml)

• Manual trigger after release PR is merged
• Creates git tag and GitHub release
• Publishes to ghcr.io/webassembly/wasi/otel
• Attests build provenance

[asteurer]

LGTM

[calebschoepp]

Thanks!