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/ARCHITECTURE.md

@@ -0,0 +1,17 @@
+# ARCHITECTURE — tinqs/builds
+
+Build artifact repo, not a codebase. There's no runtime architecture to document — the "system"
+is a flat, LFS-backed artifact store plus a manifest.
+
+## Layout
+
+- `engine/<platform>/` — engine editor binaries + their matched `GodotSharp/` C# bindings
+- `manifest.json` — exact versions/commits for each shipped artifact
+- `.gitattributes` — Git LFS rules for binaries and GodotSharp
+
+## Law
+
+Binary and `GodotSharp/` for a given engine build are a **matched pair** — always install/replace
+together. See root `README.md` for the full rule and current per-platform status table.
+
+See `architecture/` for any future per-system breakdowns (none yet — repo is single-purpose).