agents: add AGENTS.md + .agents/ scaffolding (wiki/plans/skills stubs)

Adds the root AGENTS.md entry point and minimal .agents/ skeleton
(SOUL, wiki/master-plan+ARCHITECTURE, plans/, skills/) per the
per-repo-agents-convention. Existing handoffs/ untouched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.agents/wiki/master-plan.md

@@ -0,0 +1,22 @@
+# Master plan — tinqs/builds
+
+## Current state
+
+Build artifact repo: stores engine editor binaries + matched `GodotSharp/` C# bindings for the
+Tinqs/Ariki stack, plus `manifest.json` tracking exact shipped versions. Source lives in
+`tinqs/engine`, `tinqs/ariki-game`, `tinqs/ariki-sim` — this repo only holds built output.
+
+- macOS arm64: engine 4.7, native Terrain3D module, GodotSharp shipped.
+- Windows x64: engine 4.6.5 (pre-4.7), GDExtension Terrain3D, 4.7 upgrade pending Forge —
+  see `.agents/handoffs/forge-windows-4.7.md`.
+
+## In flight
+
+- Windows 4.7 engine build + matching GodotSharp (blocked on Forge machine — see handoff).
+- Longer-term: CI (Gitea Actions) building on push and publishing here / to S3 — tracked in
+  `docs/ai/plans/build-pipeline-architecture-2026-06-07.md` (hub repo, not here).
+
+## Recently shipped
+
+- macOS arm64 rebuilt on 4.7 with native Terrain3D + agent_skinned modules, Tinqs branding restored,
+  GodotSharp regenerated to match.