engine: tune the default world to a soft program

DefaultConfig now describes a more realistic world: a moderately novel fake
(novelty 0.3), some ambient harm awareness (0.2), and a strong but imperfect
education program (programEffect 0.8) so educated students mostly, not always,
refuse. The headline shifts from 99/70/7 (a perfect program) to 100/83/21 out
of 120 (83/69/18 percent): no program >> random >> most-connected still holds,
targeting still wins by ~4x, but the program is no longer a perfect wall.
Golden values re-pinned in the engine and API tests; the preset base matches.
The forward-chance formula test now neutralises its baseline so it pins the
formula, not the tuned defaults.

internal/api/api_test.go

@@ -81,9 +81,9 @@ func TestComparisonEndpointMatchesGoldenValues(t *testing.T) {
 	// The same golden values the engine tests pin; the API must not
 	// change them in transit.
 	wantReached := map[engine.Strategy]int{
-		engine.StrategyNone:          99,
-		engine.StrategyRandom:        70,
-		engine.StrategyMostConnected: 7,
+		engine.StrategyNone:          100,
+		engine.StrategyRandom:        83,
+		engine.StrategyMostConnected: 21,
 	}
 	if len(comparison.Results) != len(wantReached) {
 		t.Fatalf("got %d results, want %d", len(comparison.Results), len(wantReached))

internal/api/scenario_test.go

@@ -29,8 +29,8 @@ func TestScenarioEndpointReturnsResultAndTopology(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if response.Result.NumReached != 7 { // the pinned golden value
-		t.Errorf("NumReached = %d, want 7", response.Result.NumReached)
+	if response.Result.NumReached != 21 { // the pinned golden value (tuned default world)
+		t.Errorf("NumReached = %d, want 21", response.Result.NumReached)
 	}
 	if response.Config != request.Config {
 		t.Errorf("config not echoed: got %+v", response.Config)