Add topics endpoint and refactor to topic-based discovery

- Add GET /topics endpoint with pagination and peer counts
- Refactor offers to support multiple topics per offer
- Add stateless authentication with AES-256-GCM
- Add bloom filter support for peer exclusion
- Update database schema for topic-based discovery
- Add comprehensive API documentation to README

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

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

src/bloom.ts

@@ -0,0 +1,62 @@
+/**
+ * Bloom filter utility for testing if peer IDs might be in a set
+ * Used to filter out known peers from discovery results
+ */
+
+export class BloomFilter {
+  private bits: Uint8Array;
+  private size: number;
+  private numHashes: number;
+
+  /**
+   * Creates a bloom filter from a base64 encoded bit array
+   */
+  constructor(base64Data: string, numHashes: number = 3) {
+    // Decode base64 to buffer
+    const buffer = Buffer.from(base64Data, 'base64');
+    this.bits = new Uint8Array(buffer);
+    this.size = this.bits.length * 8;
+    this.numHashes = numHashes;
+  }
+
+  /**
+   * Test if a peer ID might be in the filter
+   * Returns true if possibly in set, false if definitely not in set
+   */
+  test(peerId: string): boolean {
+    for (let i = 0; i < this.numHashes; i++) {
+      const hash = this.hash(peerId, i);
+      const index = hash % this.size;
+      const byteIndex = Math.floor(index / 8);
+      const bitIndex = index % 8;
+
+      if (!(this.bits[byteIndex] & (1 << bitIndex))) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /**
+   * Simple hash function (FNV-1a variant)
+   */
+  private hash(str: string, seed: number): number {
+    let hash = 2166136261 ^ seed;
+    for (let i = 0; i < str.length; i++) {
+      hash ^= str.charCodeAt(i);
+      hash += (hash << 1) + (hash << 4) + (hash << 7) + (hash << 8) + (hash << 24);
+    }
+    return hash >>> 0;
+  }
+}
+
+/**
+ * Helper to parse bloom filter from base64 string
+ */
+export function parseBloomFilter(base64: string): BloomFilter | null {
+  try {
+    return new BloomFilter(base64);
+  } catch {
+    return null;
+  }
+}