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/attachments.ts

@@ -0,0 +1,15 @@
+export * as ConfigAttachments from "./attachments"
+
+import { Schema } from "effect"
+import { PositiveInt } from "../schema"
+
+export class Image extends Schema.Class<Image>("ConfigV2.Attachments.Image")({
+  auto_resize: Schema.Boolean.pipe(Schema.optional),
+  max_width: PositiveInt.pipe(Schema.optional),
+  max_height: PositiveInt.pipe(Schema.optional),
+  max_base64_bytes: PositiveInt.pipe(Schema.optional),
+}) {}
+
+export class Info extends Schema.Class<Info>("ConfigV2.Attachments")({
+  image: Image.pipe(Schema.optional),
+}) {}