refactor: rename 'user' target to 'source' in slay-the-spire-like

Updates the card effect and intent target types from 'user' to 'source'
within the desert data files and combat effect system to maintain
consistency. Also reformat command tests to use 2-space indentation.

src/samples/slay-the-spire-like/system/combat/effects.ts

@@ -112,7 +112,7 @@ export function* getEffectTargets(
     for (const enemy of getAliveEnemies(game.value)) {
       yield enemy;
     }
-  } else if (target === "user") {
+  } else if (target === "source") {
     const entity = getCombatEntity(game.value, sourceEntityKey);
     if (entity) yield entity;
   } else if (target === "player") {