add(license): add GPLv3 license and update README.md

COPYING.assets

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+COPYING.assets
+==============
+
+This project uses a two-license structure. Please read this before
+redistributing or forking.
+
+
+CODE — under GPLv3 or later
+---------------------------
+Everything under `cli/`, `scripts/`, `.github/`, plus files at the
+repo root that are not listed under ASSETS below — is licensed under
+the GNU General Public License, version 3 or later.
+
+Full text: see the `LICENSE` file at the repo root.
+
+Additional attribution requirements under GPLv3 § 7(b) are recorded
+in the `NOTICE` file, which must be preserved with all redistributions.
+
+
+ASSETS — each image has its own free-license
+--------------------------------------------
+The following are NOT under GPLv3:
+
+  - `assets/images/*.png`      — car photos
+  - `assets/ansi/*.txt`        — pre-rendered ANSI derivatives of those photos
+  - `assets/licenses/*.json`   — per-image attribution records
+
+Every image was sourced from Wikimedia Commons or a similar free-
+culture repository, and each carries its own individual free-license,
+one of:
+
+  - Creative Commons Zero (CC0)
+  - Creative Commons Attribution (CC BY, any version)
+  - Creative Commons Attribution-ShareAlike (CC BY-SA, any version)
+  - GNU Free Documentation License (GFDL)
+  - Public Domain
+  - Free Art License
+  - Copyrighted Free Use
+
+The exact license, author, source URL, and license URL for each
+image is stored in `assets/licenses/<slug>.json`. A human-readable
+summary of all image credits is in `CREDITS.md` at the repo root.
+
+
+WHAT THIS MEANS FOR REDISTRIBUTION
+----------------------------------
+If you redistribute this project — fork it, package it, ship a
+binary bundling the assets — you MUST:
+
+  1. Include the `LICENSE` file (GPLv3) for the code.
+  2. Include the `NOTICE` file so author attribution travels with
+     the work.
+  3. Keep `assets/licenses/` intact. It is the attribution that
+     makes the images redistributable — without it, the images
+     lose their license validity.
+  4. Preserve `CREDITS.md`.
+  5. For any image licensed ShareAlike (CC BY-SA, GFDL), if you
+     modify that image, you must release the modified version
+     under the same license.
+
+If you're redistributing ONLY the CODE (not the images):
+you only need GPLv3 + NOTICE. You don't need to comply with the
+image licenses because you aren't distributing the images.
+
+
+MANIFEST AND DATABASE
+---------------------
+`manifest.json` and `data/car_database_v2.txt` are original curation
+work — the mapping of slugs to metadata, brand groupings, decade
+categorization, and the pipeline that produced them. They are under
+GPLv3, part of the code. They do not inherit the image licenses.
+
+
+CONTRIBUTING NEW IMAGES
+-----------------------
+When adding a new car via `scripts/add_car.py`, the script requires
+you to declare the license explicitly. It refuses to accept images
+under Fair Use, All Rights Reserved, NC (non-commercial), ND (no
+derivatives), or any restrictive license. This is enforced to keep
+the project fully redistributable.
+
+
+CONCERNS
+--------
+If you believe a specific image's license attribution is incorrect,
+please open an issue with the slug and the correct attribution.
+Licensing accuracy matters — we'll fix it quickly.