feat: fix travel placement bug, add theme-based alternate icons, fix animated background crash

- Fix repeat-city travel placement: use stop indices instead of global city name
  matching so Follow Team trips with repeat cities show travel correctly
- Add TravelPlacement helper and regression tests (7 tests)
- Add alternate app icons for each theme, auto-switch on theme change
- Fix index-out-of-range crash in AnimatedSportsBackground (19 configs, was iterating 20)
- Add marketing video configs, engine, and new video components
- Add docs and data exports

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

marketing-videos/src/engine/index.ts

@@ -0,0 +1,9 @@
+export { VideoFromConfig } from "./VideoFromConfig";
+export type {
+  VideoConfig,
+  SceneConfig,
+  SceneType,
+  CaptionLine,
+  Week1Configs,
+} from "./types";
+export { ASSET_KEYS } from "./types";