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/

.gitignore

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+.DS_Store
+node_modules
+.worktrees
+.sst
+.env
+.env.local
+.idea
+.vscode
+.codex
+*~
+playground
+tmp
+dist
+ts-dist
+.turbo
+**/.serena
+.serena/
+**/.omo
+.omo/
+/result
+refs
+Session.vim
+/opencode.json
+a.out
+target
+.scripts
+.direnv/
+
+# AirCoding local state
+.air/
+
+# Local dev files
+opencode-dev
+UPCOMING_CHANGELOG.md
+logs/
+*.bun-build
+tsconfig.tsbuildinfo