docs: add LEGAL.md licensing overview

Author: flyingrobots

LEGAL.md

@@ -0,0 +1,43 @@
+<!-- SPDX-License-Identifier: Apache-2.0 OR MIND-UCAL-1.0 -->
+
+# Legal Overview
+
+This document explains how licensing works in this repository. It is a summary
+only; if anything here conflicts with the full license texts, those texts
+control (`LICENSE-APACHE`, `LICENSE-MIND-UCAL`).
+
+## 1) Code
+
+- Applies to: Rust source, build scripts, shell/Python/JS tooling, binaries, Makefiles, configs used to build/run the code.
+- License: **Apache License, Version 2.0** only.  
+  See `LICENSE-APACHE`.
+- SPDX for code files: `SPDX-License-Identifier: Apache-2.0`
+
+## 2) Theory / Math / Documentation
+
+- Applies to: `docs/`, `rmg-math/`, LaTeX sources, papers/notes, other written or mathematical materials.
+- License options (your choice):
+  - Apache License, Version 2.0 **OR**
+  - MIND-UCAL License v1.0
+- SPDX for these files: `SPDX-License-Identifier: Apache-2.0 OR MIND-UCAL-1.0`
+- If you do not wish to use MIND-UCAL, you may use all theory, math, and documentation under Apache 2.0 alone. No portion of this repository requires adopting MIND-UCAL.
+
+## 3) SPDX Policy
+
+- All tracked source and documentation files must carry an SPDX header.
+- Enforcement:
+  - `scripts/ensure_spdx.sh` (pre-commit): inserts missing headers into staged files, restages, and aborts so you can review.
+  - `scripts/check_spdx.sh`: check-only helper (unused by default).
+- Patterns:
+  - Code: `Apache-2.0`
+  - Docs/math: `Apache-2.0 OR MIND-UCAL-1.0`
+- Exclusions: generated/binary assets (e.g., target/, node_modules/, PDFs, images) are not labeled.
+
+## 4) NOTICE
+
+See `NOTICE` for attribution. Apache 2.0 requires preservation of NOTICE content in redistributions that include NOTICE.
+
+## 5) No additional terms
+
+No extra terms or conditions beyond the licenses above. Unless required by law,
+all material is provided “AS IS”, without warranties or conditions of any kind.