docs: declare where the data comes from, and under what terms

The module's own Apache-2.0 licence covers its code and says nothing
about the material it fetches. STORE.yaml now carries a data_source
block (publisher, url, terms, required attribution, and bundled:
false), and MODULE.md/MODULE.de.md explain it in both languages,
including the sentence that the retrieved text does not replace the
official version.

Enforced platform-side by data_source_gap in chain_hub::store_index;
the four rules are written up in docs/architecture/store-format.md of
the platform repo.

Signed-off-by: flemming-it <sf@flemming.it>

MODULE.md

@@ -57,3 +57,22 @@ gesetze-im-internet.de: `https://www.gesetze-im-internet.de/<slug>/`.
 - Unknown slug → clear invalid-input error naming the checked URL.
 - Non-ZIP or XML-less download, HTML error pages → internal error
   with the reason; nothing HTML-shaped is ever passed downstream.
+
+## Data source
+
+gesetze-im-internet.de (BMJ / juris GmbH)
+
+Attribution: `Quelle: gesetze-im-internet.de (Bundesministerium der Justiz)`
+
+The statutes themselves are `amtliche Werke` under section 5 UrhG and
+carry no copyright. The module fetches one law per call from the public
+BMJ site and ships no corpus, so it takes no substantial part of the
+collection published there.
+
+**The returned text does not replace the official promulgation.** It
+evidences what the source served at a point in time, which is why the
+module carries the SHA-256 and the BMJ builddate in its `meta` output.
+
+## License
+
+Apache-2.0 — a Ch∆In platform module (Flemming.AI).