Add transactional event hooks

[owjs3901]

Summary

• add a typed Event contract and event-aware transaction wrapper that persists action work and the JSON outbox row together
• add Inline and Deferred subscriber registrations to plugin metadata and yeollin_plugin!
• abort failed Inline transactions, reject nested emission, and run Deferred subscribers only after commit
• add notify-driven draining with polling recovery and at-least-once retry state
• emit typed create/update/delete events from the memo example and document the operational contract

Verification

• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo test --workspace
• $env:RUSTDOCFLAGS='-D warnings'; cargo doc --workspace --no-deps
• bunx oxlint
• bun x tsc --noEmit in packages/app, apps/example-app, and every plugin
• cargo run -p yeollin-cli -- build --skip-backend from apps/example-app

QA

• no UI ships in this phase, so browser QA is not applicable
• assembled-system coverage verifies a real memo write and memo.created outbox row commit together