test(eval): bump maxTurns to 15 for claude-dedicated-tools-vs-bash

The prompt 'list every TypeScript file under src/ and tell me what
each exports' needs 1 turn for Glob + ~5 for Reads + 1 for summary.
Default maxTurns=5 was not enough; prior run threw from the SDK on
this fixture and tanked the whole periodic eval.

Bumping to 15 gives headroom. The runner now also handles max-turns
gracefully even if a future fixture underestimates, so this is belt
and suspenders.

test/fixtures/overlay-nudges.ts

@@ -253,6 +253,9 @@ export const OVERLAY_FIXTURES: OverlayFixture[] = [
     trials: 10,
     concurrency: 3,
     direction: 'lower_is_better',
+    // 5 files + summary = needs more than default 5 turns. SDK throws
+    // instead of returning a result when it hits the cap.
+    maxTurns: 15,
     setupWorkspace: (dir) => {
       fs.mkdirSync(path.join(dir, 'src'), { recursive: true });
       fs.writeFileSync(path.join(dir, 'src', 'index.ts'), "export const x = 1;\n");