Improve type safety: Replace any with proper types

Replace `candidate: any` with `candidate: RTCIceCandidateInit | null`:

Changes:
- api.ts poll() return type (line 366)
- rondevu.ts pollOffers() return type (line 827)
- IceCandidate interface (line 41)

Benefits:
- Better type safety and IntelliSense support
- Matches WebRTC spec (candidates can be null)
- Catches potential type errors at compile time
- Clearer API contracts for consumers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/rondevu.ts

@@ -824,7 +824,7 @@ export class Rondevu {
             answeredAt: number
         }>
         iceCandidates: Record<string, Array<{
-            candidate: any
+            candidate: RTCIceCandidateInit | null
             role: 'offerer' | 'answerer'
             peerId: string
             createdAt: number