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/plugin/src/example.ts

@@ -0,0 +1,18 @@
+import { Plugin } from "./index.js"
+import { tool } from "./tool.js"
+
+export const ExamplePlugin: Plugin = async (_ctx) => {
+  return {
+    tool: {
+      mytool: tool({
+        description: "This is a custom tool",
+        args: {
+          foo: tool.schema.string().describe("foo"),
+        },
+        async execute(args) {
+          return `Hello ${args.foo}!`
+        },
+      }),
+    },
+  }
+}