t5de-catalog: store and serve community product files

A Go server that takes product uploads with hub upload tokens, checks them by
t5de-api's pack rules, stores files by sha256, registers revisions with the hub
(POST /api/v1/catalog/revisions), and serves files with immutable caching;
files used only by adult revisions need an adult access token. Contract:
t5de-hub's docs/products.md.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.gitignore

@@ -0,0 +1,2 @@
+/dist/
+/data/