Add The Frontier, a second setting, and a picker to choose between them

Cold Fork is a freight yard: 29 events across two stages, a four-day cycle, and
its own relationship and skill vocabulary. src/engine/ was not touched. Adding it
needed three changes outside the engine: one save slot per pack, app.js holding
the current pack, and turn.js no longer naming the mailroom (DECISIONS #34).
build.js now handles imports wrapped across lines. A conformance suite runs over
every registered pack. DECISIONS #35 records three calls on open questions.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RxdJFbLq1rBKsUeticGV1g

test/build.test.js

@@ -36,6 +36,18 @@ test('the bundle builds, and the bundled game boots and plays', () => {
     // eslint-disable-next-line no-new-func -- running the build output is the point
     new Function(script)();
 
+    // Nothing is saved and nothing is remembered, so a build shipping more
+    // than one setting opens on the picker. Click into the first one and carry
+    // on — this exercises the front door in the real bundle, which is the one
+    // place the pack registry, the picker screen and the save slots all meet.
+    assert.ok(firstByClass(dom.root, 'screen--packs'), 'the bundled game rendered the picker');
+    assert.match(dom.root.textContent, /Corporate Ladder/, 'the packs are named');
+    assert.match(dom.root.textContent, /The Frontier/);
+
+    const start = byClass(dom.root, 'button').find((b) => /Start here|Keep playing/.test(b.textContent));
+    assert.ok(start, 'the picker offers a way in');
+    start.click();
+
     assert.ok(firstByClass(dom.root, 'screen--turn'), 'the bundled game rendered a turn');
     assert.match(dom.root.textContent, /Day 1/);
     assert.match(dom.root.textContent, /Marlene Hobb/);