feat(aircoding): AirCoding V2 baseline — deterministic multi-agent architecture

Forked from OpenCode v1.17.4 with multi-agent system:
- 5 agents: aircoding, scheduler, worker, architect, reviewer
- Deterministic DAG scheduling engine (coordinator_tick)
- Tool whitelists as hard enforcement
- AirCoding validation plugin
- V1 requirements: C4 docs, ADR, AGENTS.md, debug-log.md
- Design documents in docs/

packages/core/src/config/plugin.ts

@@ -0,0 +1,13 @@
+export * as ConfigPlugin from "./plugin"
+
+import { Schema } from "effect"
+
+export class Entry extends Schema.Class<Entry>("ConfigV2.Plugin.Entry")({
+  package: Schema.String,
+  options: Schema.Record(Schema.String, Schema.Unknown).pipe(Schema.optional),
+}) {}
+
+export const Plugin = Schema.Union([Schema.String, Entry])
+export type Plugin = typeof Plugin.Type
+
+export const Plugins = Plugin.pipe(Schema.Array)