feat(plugin): intercept user prompts before admission - #45550

Summary

• add ctx.session.hook("prompt", ...) for transforming text, files, agent mentions, skills, metadata, and delivery before durable admission
• prepare drafts in one location scope after plugin readiness, then use normal attachment/skill resolution
• bypass hooks and payload resolution for already-admitted IDs while retaining concurrent first-admission-wins behavior
• keep preparation interruptible and staged reverts intact on retries or preparation failure; typed rejection remains out of scope

Testing

• bun test test/session-*.test.ts test/plugin-hooks.test.ts test/plugin/promise.test.ts in packages/core: 541 passing across 35 files
• core and plugin package typechecks, including readonly-ID and provider-filter type tests
• repository-wide pre-push typecheck: 33 successful tasks
• thermo-nuclear maintainability review and fix/review loop performed without subagents; no remaining blockers found