Set up project structure, source files, and architecture docs

- Copy core source from alkhub_ts/packages/core/pubsub/ with import path fixups
  (typed_event_target.ts → types.ts, .ts → .js extensions)
- Make PubSubPublishArgsByKey exported (was private type, needed by barrel)
- Add package.json with sub-path exports and optional peer deps (ioredis)
- Add tsup.config.ts with multi-entry + splitting for tree-shaking
- Add tsconfig.json, vitest.config.ts, .gitignore
- Add AGENTS.md with project conventions and adapter checklist
- Add architecture docs following taskgraph/alkhub pattern:
  docs/architecture/README.md, api-surface.md, event-targets.md,
  iroh-transport.md, build-distribution.md
- Add ADRs: 001-graphql-yoga-fork, 002-tree-shake-pattern
- Copy migration research doc to docs/research/migration.md
- Dual-license MIT OR Apache-2.0 (matching taskgraph)

src/index.ts

@@ -0,0 +1,4 @@
+export { createPubSub, type PubSub, type PubSubConfig, type PubSubEvent, type PubSubEventTarget, type PubSubPublishArgsByKey } from "./create_pubsub.js";
+export { type TypedEvent, type TypedEventTarget, type TypedEventListener, type TypedEventListenerObject, type TypedEventListenerOrEventListenerObject } from "./types.js";
+export { filter, map, pipe } from "./operators.js";
+export { Repeater } from "@repeaterjs/repeater";