catalog: tags duplicate licence/publisher and have drifted

[TMHSDigital]

Tags that restate license or publisher are unreliable filters:

• cc0 is missing on 20 of the 145 CC0 entries; mit is on only 6 of 41 MIT entries.
• cc0 is set on two varies entries (blenderkit, universal-lpc-generator); public-domain on openclipart (which is CC0).
• kenney is missing on 14 Kenney entries.
• Plain duplicates: games-ok (filmmusic-ende) vs game-ok (tallbeard-abstraction-music-loop-bundle); ps1 vs psx; godot (9) vs godot-4 (19).

Fix: drop licence/publisher tags and have the build derive them (or filter on the fields directly). Pick one spelling for each duplicate pair.

[TMHSDigital]

Partly done in #49: the plain duplicate pairs are merged (games-ok, psx), godot-4 entries also carry godot, cc0 is gone from the two varies entries and public-domain from openclipart; V19 (site/value-aliases.json) keeps retired spellings out. Still open: the policy question of whether tags should restate license and publisher at all (the drift: cc0 missing on 20 CC0 entries, mit on only 6 of 41 MIT entries, kenney missing on 14).