feat: add audios table and ElevenLabs TTS endpoint

- New audios table with voice params, S3 link, alignment JSON
- POST /api/audios/generate calls ElevenLabs with-timestamps, uploads to S3
- GET/PATCH/DELETE /api/audios endpoints
- Requires ELEVENLABS_API_KEY env var

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/db-migrate.js

@@ -494,6 +494,62 @@ async function migrate() {
        AND bbox_x IS NULL
   `).catch(() => {});
 
+  // user_pair_progress
+  await query(`
+    CREATE TABLE IF NOT EXISTS user_pair_progress (
+      user_id       UUID    NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+      pair_id       UUID    NOT NULL REFERENCES pairs(id) ON DELETE CASCADE,
+      seen_count    INTEGER NOT NULL DEFAULT 1,
+      correct_count INTEGER NOT NULL DEFAULT 0,
+      wrong_count   INTEGER NOT NULL DEFAULT 0,
+      last_seen_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+      PRIMARY KEY (user_id, pair_id)
+    )
+  `);
+
+  await query(`
+    CREATE OR REPLACE FUNCTION update_last_seen_at()
+    RETURNS TRIGGER AS $$
+    BEGIN NEW.last_seen_at = NOW(); RETURN NEW; END;
+    $$ LANGUAGE plpgsql
+  `);
+
+  await query(`
+    DROP TRIGGER IF EXISTS user_pair_progress_last_seen_at ON user_pair_progress;
+    CREATE TRIGGER user_pair_progress_last_seen_at
+      BEFORE UPDATE ON user_pair_progress
+      FOR EACH ROW EXECUTE FUNCTION update_last_seen_at()
+  `);
+
+  // audios
+  await query(`
+    CREATE TABLE IF NOT EXISTS audios (
+      id                UUID        PRIMARY KEY DEFAULT gen_random_uuid(),
+      status            VARCHAR(20) NOT NULL DEFAULT 'generated'
+                          CHECK (status IN ('generated', 'published', 'blocked')),
+      text              TEXT,
+      audio_link        TEXT,
+      alignment         JSONB,
+      voice_id          TEXT,
+      model_id          TEXT,
+      speed             NUMERIC(4,2),
+      stability         NUMERIC(4,2),
+      similarity_boost  NUMERIC(4,2),
+      style             NUMERIC(4,2),
+      published_at      TIMESTAMPTZ,
+      blocked_at        TIMESTAMPTZ,
+      created_at        TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+      updated_at        TIMESTAMPTZ NOT NULL DEFAULT NOW()
+    )
+  `);
+
+  await query(`
+    DROP TRIGGER IF EXISTS audios_updated_at ON audios;
+    CREATE TRIGGER audios_updated_at
+      BEFORE UPDATE ON audios
+      FOR EACH ROW EXECUTE FUNCTION update_updated_at()
+  `);
+
   // ── Migrate old {{uuid}} placeholders → new {{label.w:uuid}} / {{label.o:uuid}} ──
   await migratePlaceholders();