pikachat-openclaw: harden reactions and typecheck against OpenClaw

[futurepaul]

Summary

• keep the Nostr heart fallback (❤️) when reaction content is empty, while avoiding confusing agent context
• convert inbound kind=7 reactions to passive session context using runtime.system.enqueueSystemEvent (aligned with default OpenClaw channel behavior)
• await async sidecar send calls at all callsites to avoid unhandled rejection risk after PR pikachat-openclaw: surface event_id in agent context, filter inbound reactions (built on #342) #361 changes
• tighten extension typing against OpenClaw SDK interfaces (message actions/tool factories/results), remove as any tool registration casts, and add openclaw as a dev dependency for real SDK type checking
• add focused reaction helper tests

Why

PR #361 improved message-id semantics and action support, but introduced two quality risks:

1. async sidecar sends could reject without being handled
2. reaction events were dispatched through normal reply flow instead of passive context

This follow-up keeps the intended behavior while matching OpenClaw conventions and strict typing.

Testing

• pnpm -C pikachat-openclaw/openclaw/extensions/pikachat-openclaw typecheck
• cd pikachat-openclaw/openclaw/extensions/pikachat-openclaw && pnpm dlx tsx --test src/*.test.ts