refactor(schema): extract public event definitions

[kitlangton]

Summary

• define public events with pure schema-owned definitions and explicit immutable domain inventories
• derive latest public manifests and complete durable type.version indexes without import-time registration
• move durable Session, legacy Session/Permission, and Todo event schemas into @opencode-ai/schema
• rewire Core replay/publishing and server/OpenAPI generation to consume explicit manifests
• preserve wire event names and type-only projector dispatch while retaining historical durable codecs

SDK impact

• adds the existing ide.installed event to generated unions; it was previously omitted by import-order-dependent registry snapshots
• no existing generated event shape is removed or changed

Verification

• all 24 workspace typecheck tasks passed
• 81 focused event, projection, manifest, and API tests passed
• file-scoped oxlint passed with existing event-runtime warnings and 0 errors
• repeated SDK generation was deterministic
• git diff --check passed

Follow-up

• projector dispatch remains keyed by event type; exact type+version projector dispatch is intentionally deferred
• live-only event definitions whose payload models remain runtime-owned are indexed explicitly but remain colocated with their current domains