Refactor peer connection state machine into separate files

Split the monolithic peer.ts file into a modular state-based architecture:
- Created separate files for each state class (idle, creating-offer, waiting-for-answer, answering, exchanging-ice, connected, failed, closed)
- Extracted shared types into types.ts
- Extracted base PeerState class into state.ts
- Updated peer/index.ts to import state classes instead of defining them inline
- Made close() method async to support dynamic imports and avoid circular dependencies
- Used dynamic imports in state transitions to prevent circular dependency issues

This improves code organization, maintainability, and makes each state's logic easier to understand and test.

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

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

src/peer/answering-state.ts

@@ -0,0 +1,56 @@
+import { PeerState } from './state.js';
+import type { PeerOptions } from './types.js';
+import type RondevuPeer from './index.js';
+
+/**
+ * Answering an offer and sending to server
+ */
+export class AnsweringState extends PeerState {
+  constructor(peer: RondevuPeer) {
+    super(peer);
+  }
+
+  get name() { return 'answering'; }
+
+  async answer(offerId: string, offerSdp: string, options: PeerOptions): Promise<void> {
+    try {
+      this.peer.role = 'answerer';
+      this.peer.offerId = offerId;
+
+      // Set remote description
+      await this.peer.pc.setRemoteDescription({
+        type: 'offer',
+        sdp: offerSdp
+      });
+
+      // Create answer
+      const answer = await this.peer.pc.createAnswer();
+      await this.peer.pc.setLocalDescription(answer);
+
+      // Send answer to server immediately (don't wait for ICE)
+      await this.peer.offersApi.answer(offerId, answer.sdp!);
+
+      // Enable trickle ICE - send candidates as they arrive
+      this.peer.pc.onicecandidate = async (event: RTCPeerConnectionIceEvent) => {
+        if (event.candidate && offerId) {
+          const candidateData = event.candidate.toJSON();
+          if (candidateData.candidate && candidateData.candidate !== '') {
+            try {
+              await this.peer.offersApi.addIceCandidates(offerId, [candidateData]);
+            } catch (err) {
+              console.error('Error sending ICE candidate:', err);
+            }
+          }
+        }
+      };
+
+      // Transition to exchanging ICE
+      const { ExchangingIceState } = await import('./exchanging-ice-state.js');
+      this.peer.setState(new ExchangingIceState(this.peer, offerId, options));
+    } catch (error) {
+      const { FailedState } = await import('./failed-state.js');
+      this.peer.setState(new FailedState(this.peer, error as Error));
+      throw error;
+    }
+  }
+}