feat(db-migrate): add DROP_EXISTING_TABLES support

When DROP_EXISTING_TABLES=true, drop all existing tables before running migrations.

crates/db-migrate/src/main.rs

@@ -21,6 +21,14 @@ async fn main() -> Result<()> {
         .context("Failed to connect to database")?;
     tracing::info!("Connected to database");
 
+    let drop_existing = std::env::var("DROP_EXISTING_TABLES")
+        .unwrap_or_default()
+        .to_lowercase();
+    
+    if drop_existing == "true" || drop_existing == "1" || drop_existing == "yes" {
+        drop_all_tables(&pool).await?;
+    }
+
     let migrations_dir = std::env::var("MIGRATIONS_DIR")
         .unwrap_or_else(|_| "/migrations".to_string());
 
@@ -30,6 +38,30 @@ async fn main() -> Result<()> {
     Ok(())
 }
 
+async fn drop_all_tables(pool: &sqlx::PgPool) -> Result<()> {
+    tracing::warn!("DROP_EXISTING_TABLES is enabled - dropping all tables!");
+
+    let rows: Vec<(String,)> = sqlx::query_as("SELECT tablename FROM pg_tables WHERE schemaname = 'public'")
+        .fetch_all(pool)
+        .await?;
+
+    if rows.is_empty() {
+        tracing::info!("No tables to drop");
+        return Ok(());
+    }
+
+    tracing::info!("Found {} tables to drop", rows.len());
+
+    for (table_name,) in rows {
+        let sql = format!("DROP TABLE IF EXISTS \"{}\" CASCADE", table_name);
+        tracing::info!("Dropping table: {}", table_name);
+        sqlx::raw_sql(&sql).execute(pool).await?;
+    }
+
+    tracing::info!("All tables dropped successfully");
+    Ok(())
+}
+
 async fn run_migrations(pool: &sqlx::PgPool, migrations_dir: &str) -> Result<()> {
     let migrations_path = Path::new(migrations_dir);