Adds Top Rivalries widget to landing page and Rivals section to bot
profiles, completing the platform integration for the automatic rivalry
detection system.
## Changes
- web/src/pages/home.ts: fetch rivalries data and render Top Rivalries card
- web/src/pages/bot-profile.ts: add Rivals section filtered to this bot
- web/src/styles/components.css: add rivalry list/item styles
## Plan §13.5 Platform Integration
✅ Rivalry widget on landing page with head-to-head records
✅ Bot profile pages show Rivals section with filtered rivalries
✅ Narratives already implemented via buildRivalryNarrative()
Closes: bf-2quf
2480104214