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/opencode/test/fixture/skills/index.json

@@ -0,0 +1,6 @@
+{
+  "skills": [
+    { "name": "agents-sdk", "description": "Cloudflare Agents SDK", "files": ["SKILL.md", "references/callable.md"] },
+    { "name": "cloudflare", "description": "Cloudflare Platform Skill", "files": ["SKILL.md"] }
+  ]
+}