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/

patches/gcp-metadata@8.1.2.patch

@@ -0,0 +1,14 @@
+diff --git a/build/src/index.js b/build/src/index.js
+--- a/build/src/index.js
++++ b/build/src/index.js
+@@ -323,6 +323,10 @@ async function isAvailable() {
+         if (process.env.DEBUG_AUTH) {
+             console.info(err);
+         }
++        // Promise.any() rejects with AggregateError when neither metadata host
++        // is available. This is expected outside GCP, not a warning condition.
++        if (err instanceof AggregateError)
++            return false;
+         if (err.type === 'request-timeout') {
+             // If running in a GCP environment, metadata endpoint should return
+             // within ms.