Use SyncEvent service at event call sites

[kitlangton]

Summary

• Replace v2 event emissions in Effect services with yielded SyncEvent.Service.run calls.
• Preserve the existing OPENCODE_EXPERIMENTAL_EVENT_SYSTEM guard for v2 dual-write events.
• Keep current bypass behavior for agent/model switch events by running those sync events directly.

Testing

• bun typecheck from packages/opencode
• bun test --timeout 5000 test/session/compaction.test.ts -t "creates a compaction user message and part"
• bun test --timeout 5000 test/session/processor-effect.test.ts -t "publish retry status updates|capture llm input cleanly"
• bun test --timeout 5000 test/session/prompt.test.ts -t "switch|shell|prompt"
• bunx prettier --check ... for changed files
• bunx oxlint ... for changed files (existing warnings only, no errors)
• pre-push bun turbo typecheck

Stack

1. Use SyncEvent service at event call sites #26782 👈 current
2. Drop EventV2 run facade #26783