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

content/frontier/characters.js

@@ -0,0 +1,43 @@
+// Cold Fork, as staffed.
+//
+// `description` is pure colour — the engine never reads it. What it does read
+// is `startingRelationship`, where a character departs from the pack defaults.
+// Nobody in a freight yard trusts a new hand on sight, and Dutch has had the
+// good runs to himself for two years and can count.
+
+export const characters = [
+  {
+    id: 'hollis',
+    name: 'Hollis Vane',
+    title: 'Vane & Co. Freight',
+    role_type: 'boss',
+    description:
+      'Owns the outfit, the yard, and the note on both. Settles up in the ' +
+      'doorway of the office rather than inside it, which saves having to ' +
+      'offer anyone a chair.',
+    startingRelationship: { trusts_you: 35 },
+  },
+  {
+    id: 'dutch',
+    name: 'Dutch Rennels',
+    title: 'Teamster',
+    role_type: 'rival',
+    description:
+      'Two years on the Ridge road and has driven it in every kind of weather ' +
+      'there is, as he will tell you. Keeps his own tally of who took which ' +
+      'run, in a book, in pencil.',
+    startingRelationship: { trusts_you: 30, wary_of_you: 25 },
+  },
+  {
+    id: 'ward',
+    name: 'Marshal Ward',
+    title: 'Town Marshal',
+    role_type: 'authority',
+    description:
+      'Came to Cold Fork to retire and has been six years about it. Knows who ' +
+      'owes the store and how much, and considers that most of the job.',
+    startingRelationship: { trusts_you: 25, wary_of_you: 30 },
+  },
+];
+
+export default characters;