feat: add V2 database migration for D1

Add migration to create V2 tables:
- offers (with ICE candidates)
- usernames (with Ed25519 public keys)
- services (with service discovery)
- service_index (privacy layer)

Applied to production D1 database: rondevu-offers

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

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

migrations/0005_v2_schema.sql

@@ -0,0 +1,83 @@
+-- V2 Migration: Add offers, usernames, and services tables
+
+-- Offers table (replaces sessions)
+CREATE TABLE IF NOT EXISTS offers (
+  id TEXT PRIMARY KEY,
+  peer_id TEXT NOT NULL,
+  sdp TEXT NOT NULL,
+  created_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL,
+  last_seen INTEGER NOT NULL,
+  secret TEXT,
+  answerer_peer_id TEXT,
+  answer_sdp TEXT,
+  answered_at INTEGER
+);
+
+CREATE INDEX IF NOT EXISTS idx_offers_peer ON offers(peer_id);
+CREATE INDEX IF NOT EXISTS idx_offers_expires ON offers(expires_at);
+CREATE INDEX IF NOT EXISTS idx_offers_last_seen ON offers(last_seen);
+CREATE INDEX IF NOT EXISTS idx_offers_answerer ON offers(answerer_peer_id);
+
+-- ICE candidates table
+CREATE TABLE IF NOT EXISTS ice_candidates (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  offer_id TEXT NOT NULL,
+  peer_id TEXT NOT NULL,
+  role TEXT NOT NULL CHECK(role IN ('offerer', 'answerer')),
+  candidate TEXT NOT NULL,
+  created_at INTEGER NOT NULL,
+  FOREIGN KEY (offer_id) REFERENCES offers(id) ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS idx_ice_offer ON ice_candidates(offer_id);
+CREATE INDEX IF NOT EXISTS idx_ice_peer ON ice_candidates(peer_id);
+CREATE INDEX IF NOT EXISTS idx_ice_created ON ice_candidates(created_at);
+
+-- Usernames table
+CREATE TABLE IF NOT EXISTS usernames (
+  username TEXT PRIMARY KEY,
+  public_key TEXT NOT NULL UNIQUE,
+  claimed_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL,
+  last_used INTEGER NOT NULL,
+  metadata TEXT,
+  CHECK(length(username) >= 3 AND length(username) <= 32)
+);
+
+CREATE INDEX IF NOT EXISTS idx_usernames_expires ON usernames(expires_at);
+CREATE INDEX IF NOT EXISTS idx_usernames_public_key ON usernames(public_key);
+
+-- Services table
+CREATE TABLE IF NOT EXISTS services (
+  id TEXT PRIMARY KEY,
+  username TEXT NOT NULL,
+  service_fqn TEXT NOT NULL,
+  offer_id TEXT NOT NULL,
+  created_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL,
+  is_public INTEGER NOT NULL DEFAULT 0,
+  metadata TEXT,
+  FOREIGN KEY (username) REFERENCES usernames(username) ON DELETE CASCADE,
+  FOREIGN KEY (offer_id) REFERENCES offers(id) ON DELETE CASCADE,
+  UNIQUE(username, service_fqn)
+);
+
+CREATE INDEX IF NOT EXISTS idx_services_username ON services(username);
+CREATE INDEX IF NOT EXISTS idx_services_fqn ON services(service_fqn);
+CREATE INDEX IF NOT EXISTS idx_services_expires ON services(expires_at);
+CREATE INDEX IF NOT EXISTS idx_services_offer ON services(offer_id);
+
+-- Service index table (privacy layer)
+CREATE TABLE IF NOT EXISTS service_index (
+  uuid TEXT PRIMARY KEY,
+  service_id TEXT NOT NULL,
+  username TEXT NOT NULL,
+  service_fqn TEXT NOT NULL,
+  created_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL,
+  FOREIGN KEY (service_id) REFERENCES services(id) ON DELETE CASCADE
+);
+
+CREATE INDEX IF NOT EXISTS idx_service_index_username ON service_index(username);
+CREATE INDEX IF NOT EXISTS idx_service_index_expires ON service_index(expires_at);