fix: always merge evolutionTree/generators with defaults on load

Server saves don't store all node fields (branch, cost, effect, etc.).
migrateSave now always rebuilds tree from DEFAULT_EVOLUTION_TREE,
preserving unlocked state from the save. Fixes empty evolution tree.

Frontend/src/lib/components/EvolutionTree.svelte

@@ -44,13 +44,7 @@
 	let activeBranch = $state<Branch>('ponte');
 
 	let branchConfig = $derived(BRANCH_CONFIG[activeBranch]);
-	let branchNodes = $derived(game.state.evolutionTree.filter((n: any) => n.branch === activeBranch));
+	let branchNodes = $derived(game.state.evolutionTree.filter((n) => n.branch === activeBranch));
-
-	// Debug — remove after fix confirmed
-	$effect(() => {
-		const tree = game.state.evolutionTree;
-		console.log('[EvolutionTree] tree length:', tree.length, 'activeBranch:', activeBranch, 'filtered:', tree.filter((n: any) => n.branch === activeBranch).length, 'first node:', tree[0] ? { id: tree[0].id, branch: tree[0].branch } : 'empty');
-	});
 	let spentDna = $derived(getSpentDna(game.state.evolutionTree));
 	let hasUnlocked = $derived(spentDna > 0);
 	let resetCost = $derived(getTreeResetCost(game.state));

Frontend/src/lib/core/migrateSave.ts

@@ -23,6 +23,15 @@ export function migrateSave(raw: Record<string, unknown>): GameState {
   // Futures migrations :
   // if (version < 3) state = migrateV2toV3(state);
 
+  // Always rebuild tree & generators from defaults — the server/localStorage
+  // may not store all fields (branch, cost, effect, baseProduction, etc.)
+  state.evolutionTree = mergeEvolutionTree(
+    state.evolutionTree as Array<Record<string, unknown>> | undefined
+  );
+  state.generators = mergeGenerators(
+    state.generators as Array<Record<string, unknown>> | undefined
+  );
+
   return state as unknown as GameState;
 }