Initial commit: AirCoding V1.0.0 Alpha architecture baseline

Complete architecture document set with multi-model review remediation:
- Frozen interface contracts, runtime semantics, DB schemas
- Event/tool/error/provider registries
- Scheduler and main agent state machines
- C4 module/code views, solution architecture, baseline V1
- Multi-model review reports and joint assessment
- Phase-gate remediation complete (P0/P1/P2/UX resolved)
- Implementation plan with T-000A through T-045
- Reference folders kept as placeholders only

AirPlan/docs/architecture/adr/ADR-0009-target-linux-first-with-tiered-platform-support.md

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+# ADR-0009: Target Linux First With Tiered Platform Support
+
+- Status: Accepted
+- Date: 2026-05-27
+
+## Context
+
+AirCoding's first deep workflow targets C++ development and local agent execution, which depend heavily on POSIX shell/process/filesystem semantics and local toolchains.
+
+## Decision
+
+Use Linux x86_64 as tier-1 MVP platform, Linux arm64 and WSL2 as tier-2, macOS as experimental, and Windows native as experimental/post-MVP.
+
+MVP shell/process/C++ workflows target POSIX-like Linux behavior.
+
+## Consequences
+
+- Release gates block on tier-1 Linux.
+- Platform detection and path classification must be platform-aware.
+- Windows native deep support and MSVC workflows are deferred.
+- VibeBox ARM Linux remains compatible as a downstream branch but does not define mainline MVP release blockers.