feat: Implement content-based offer IDs with SHA-256 hashing

- Added hash-id.ts utility for SHA-256 content hashing
- Offer IDs now generated from hash of {sdp, topics} (sorted)
- Removed peerId from hash (inferred from authentication)
- Server generates deterministic IDs for idempotent offer creation
- Updated SQLite and D1 storage implementations
- Removed optional id field from CreateOfferRequest
- Same offer content always produces same ID

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

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

src/config.ts

@@ -0,0 +1,51 @@
+import { generateSecretKey } from './crypto.ts';
+
+/**
+ * Application configuration
+ * Reads from environment variables with sensible defaults
+ */
+export interface Config {
+  port: number;
+  storageType: 'sqlite' | 'memory';
+  storagePath: string;
+  corsOrigins: string[];
+  version: string;
+  authSecret: string;
+  offerDefaultTtl: number;
+  offerMaxTtl: number;
+  offerMinTtl: number;
+  cleanupInterval: number;
+  maxOffersPerRequest: number;
+  maxTopicsPerOffer: number;
+}
+
+/**
+ * Loads configuration from environment variables
+ */
+export function loadConfig(): Config {
+  // Generate or load auth secret
+  let authSecret = process.env.AUTH_SECRET;
+  if (!authSecret) {
+    authSecret = generateSecretKey();
+    console.warn('WARNING: No AUTH_SECRET provided. Generated temporary secret:', authSecret);
+    console.warn('All peer credentials will be invalidated on server restart.');
+    console.warn('Set AUTH_SECRET environment variable to persist credentials across restarts.');
+  }
+
+  return {
+    port: parseInt(process.env.PORT || '3000', 10),
+    storageType: (process.env.STORAGE_TYPE || 'sqlite') as 'sqlite' | 'memory',
+    storagePath: process.env.STORAGE_PATH || ':memory:',
+    corsOrigins: process.env.CORS_ORIGINS
+      ? process.env.CORS_ORIGINS.split(',').map(o => o.trim())
+      : ['*'],
+    version: process.env.VERSION || 'unknown',
+    authSecret,
+    offerDefaultTtl: parseInt(process.env.OFFER_DEFAULT_TTL || '60000', 10),
+    offerMaxTtl: parseInt(process.env.OFFER_MAX_TTL || '86400000', 10),
+    offerMinTtl: parseInt(process.env.OFFER_MIN_TTL || '60000', 10),
+    cleanupInterval: parseInt(process.env.CLEANUP_INTERVAL || '60000', 10),
+    maxOffersPerRequest: parseInt(process.env.MAX_OFFERS_PER_REQUEST || '100', 10),
+    maxTopicsPerOffer: parseInt(process.env.MAX_TOPICS_PER_OFFER || '50', 10),
+  };
+}