Add database initialization script

- Add database/init.sql with schema
- Mount init.sql in docker-compose for auto-initialization
- PostgreSQL will run this on first startup

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

database/init.sql

@@ -0,0 +1,35 @@
+-- PriceGhost Database Schema
+
+-- Users table
+CREATE TABLE IF NOT EXISTS users (
+  id SERIAL PRIMARY KEY,
+  email VARCHAR(255) UNIQUE NOT NULL,
+  password_hash VARCHAR(255) NOT NULL,
+  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Products table
+CREATE TABLE IF NOT EXISTS products (
+  id SERIAL PRIMARY KEY,
+  user_id INTEGER REFERENCES users(id) ON DELETE CASCADE,
+  url TEXT NOT NULL,
+  name VARCHAR(255),
+  image_url TEXT,
+  refresh_interval INTEGER DEFAULT 3600,
+  last_checked TIMESTAMP,
+  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  UNIQUE(user_id, url)
+);
+
+-- Price history table
+CREATE TABLE IF NOT EXISTS price_history (
+  id SERIAL PRIMARY KEY,
+  product_id INTEGER REFERENCES products(id) ON DELETE CASCADE,
+  price DECIMAL(10,2) NOT NULL,
+  currency VARCHAR(10) DEFAULT 'USD',
+  recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Index for faster price history queries
+CREATE INDEX IF NOT EXISTS idx_price_history_product_date
+ON price_history(product_id, recorded_at);