Adopt TRSL V1C1 license; link ground-game and target-revenue sister repos

INTENT.md

@@ -77,6 +77,14 @@ game.
 > No concept becomes canonical merely because it looks general. It becomes
 > canonical after surviving a second concrete use.
 
+## Sister repositories
+
+- **`ground-game`** — the authoritative home of the GROUND boardgame itself
+  (rules, editions, content). Clay-Borg implements the engine that simulates
+  it; game-semantics questions defer to that repo.
+- **`target-revenue`** — the canonical home of the Target Revenue Framework
+  and the TRSL license text this repo is released under.
+
 ## Provenance
 
 This intent is distilled from the fuller architectural exploration in