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/state.ts

@@ -0,0 +1,41 @@
+import type { PeerOptions } from './types.js';
+import type RondevuPeer from './index.js';
+
+/**
+ * Base class for peer connection states
+ * Implements the State pattern for managing WebRTC connection lifecycle
+ */
+export abstract class PeerState {
+  constructor(protected peer: RondevuPeer) {}
+
+  abstract get name(): string;
+
+  async createOffer(options: PeerOptions): Promise<string> {
+    throw new Error(`Cannot create offer in ${this.name} state`);
+  }
+
+  async answer(offerId: string, offerSdp: string, options: PeerOptions): Promise<void> {
+    throw new Error(`Cannot answer in ${this.name} state`);
+  }
+
+  async handleAnswer(sdp: string): Promise<void> {
+    throw new Error(`Cannot handle answer in ${this.name} state`);
+  }
+
+  async handleIceCandidate(candidate: any): Promise<void> {
+    // ICE candidates can arrive in multiple states, so default is to add them
+    if (this.peer.pc.remoteDescription) {
+      await this.peer.pc.addIceCandidate(new RTCIceCandidate(candidate));
+    }
+  }
+
+  cleanup(): void {
+    // Override in states that need cleanup
+  }
+
+  async close(): Promise<void> {
+    this.cleanup();
+    const { ClosedState } = await import('./closed-state.js');
+    this.peer.setState(new ClosedState(this.peer));
+  }
+}