refactor(schema): distinguish published event durability

[kitlangton]

Summary

• derive published event durability from each event definition
• require exact durable commit metadata and forbid it on live events
• separate Core pre-commit payloads from published payloads and regenerate SDK event types

Verification

• bun turbo typecheck
• bun test test/event.test.ts in packages/core
• bun test test/event.test.ts test/legacy-event.test.ts in packages/schema
• bun test --timeout 30000 test/server/httpapi-public-openapi.test.ts test/v2/session-message-updater.test.ts in packages/opencode
• file-scoped Oxlint, Prettier, generated drift check, and git diff --check