feat: pictures table, Hetzner S3 upload/delete, auto-migration

- pictures table with UUID, status enum, timestamps, blurhash, design
- Auto-trigger updates updated_at on every row change
- POST /api/pictures/:id/upload  → upload file to Hetzner snakkimo bucket
- DELETE /api/pictures/:id       → removes DB row + Hetzner file
- PATCH /api/pictures/:id        → auto-sets published/blocked timestamps
- Migration runs on every server start (idempotent)

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

src/db-migrate.js

@@ -0,0 +1,40 @@
+const { query } = require('./db');
+
+async function migrate() {
+  await query(`
+    CREATE TABLE IF NOT EXISTS pictures (
+      id                      UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+      status                  VARCHAR(20)  NOT NULL DEFAULT 'uploaded'
+                                CHECK (status IN ('uploaded', 'published', 'blocked')),
+      blocked_reason          VARCHAR(20)  CHECK (blocked_reason IN ('regenerate', 'not_to_use')),
+      generation_prompt       TEXT,
+      generation_timestamp    TIMESTAMPTZ,
+      generation_duration_s   NUMERIC(10,3),
+      published_timestamp     TIMESTAMPTZ,
+      blocked_timestamp       TIMESTAMPTZ,
+      blurhash                TEXT,
+      picture_link            TEXT,
+      design                  TEXT,
+      created_at              TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+      updated_at              TIMESTAMPTZ NOT NULL DEFAULT NOW()
+    )
+  `);
+
+  await query(`
+    CREATE OR REPLACE FUNCTION update_updated_at()
+    RETURNS TRIGGER AS $$
+    BEGIN NEW.updated_at = NOW(); RETURN NEW; END;
+    $$ LANGUAGE plpgsql
+  `);
+
+  await query(`
+    DROP TRIGGER IF EXISTS pictures_updated_at ON pictures;
+    CREATE TRIGGER pictures_updated_at
+      BEFORE UPDATE ON pictures
+      FOR EACH ROW EXECUTE FUNCTION update_updated_at()
+  `);
+
+  console.log('Migration complete: pictures table ready');
+}
+
+module.exports = migrate;