Add lifecycle-aware view transitions

[samuel-williams-shopify]

Summary

• add a connection-scoped AbortSignal directly to ViewElement for listeners and asynchronous work
• add the optional transitionView helper through @socketry/live/Transition
• make transitions progressive enhancements whose updates always execute exactly once
• skip active visual transitions when their owning view disconnects
• document lifecycle cleanup, asynchronous readiness, stable layout, nested transitions, and reduced motion
• test transition support, fallbacks, failure handling, cancellation, and reconnection

morph() remains synchronous; this change does not alter Live update, reply, or dispatch semantics.

Validation

• npm test
• package self-import of @socketry/live/Transition
• npm pack --dry-run
• git diff --check

[samuel-williams-shopify]

Closing this for now. The lifecycle signal and View Transition coordination can remain at the application layer until we have another concrete consumer that clarifies the right shared abstraction.