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/public/ASSET_README.md

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+# Asset Placeholder Directory
+
+Replace these placeholders with real assets before rendering final videos.
+
+## Screen Recordings (`screenrecs/`)
+Record these on-device using the SportsTime app:
+
+| File | Description | Screen to Record |
+|------|-------------|-----------------|
+| `date_range.mp4` | Picking dates in trip wizard | Trip Wizard → Date Range step |
+| `follow_team.mp4` | Following a team flow | Trip Wizard → Follow Team mode |
+| `by_games.mp4` | Browsing by games | Trip Wizard → By Games mode |
+| `route_generated.mp4` | Route result appearing | Trip Detail → after planning |
+| `poll_create.mp4` | Creating a group poll | Trip Options → Share/Poll |
+| `tracker.mp4` | Stadium tracker/bucket list | Profile → Stadium Tracker |
+
+**Recording tips:**
+- Use iPhone screen recording (Settings → Control Center)
+- Portrait orientation, 1080x1920 native
+- 5-10 seconds per clip
+- Clean, smooth taps (no fumbling)
+
+## Overlays (`overlays/`)
+
+| File | Description |
+|------|-------------|
+| `imessage_bg.png` | iMessage background texture (optional) |
+| `chat_bubbles.png` | Chat bubble overlay (optional) |
+| `vote_bubbles.png` | Vote notification overlay (optional) |
+
+## B-Roll (`broll/`)
+
+| File | Description | Source |
+|------|-------------|--------|
+| `highway.mp4` | Highway driving footage | Stock/Pexels |
+| `city.mp4` | City skyline/aerial | Stock/Pexels |
+| `stadium.mp4` | Stadium exterior | Stock/Pexels |
+
+**Note:** B-roll is optional. Videos render with placeholder scenes when assets are missing.