Fix newbook_current_rates column names + rollback on failed date

- schema defined gross_rate/net_rate but every query (fetch job,
  bookability, competitors) uses rate_gross/rate_net — rename the
  columns, with an idempotent DO-block migration for existing tables
- roll back the session when a date fails so one bad statement no
  longer poisons the whole sync run (every subsequent write was dying
  with 'current transaction is aborted')

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/schema.sql

@@ -158,13 +158,23 @@ CREATE TABLE IF NOT EXISTS newbook_current_rates (
     id              SERIAL PRIMARY KEY,
     category_id     VARCHAR(50) NOT NULL,
     rate_date       DATE NOT NULL,
-    gross_rate      DECIMAL(12,2),
-    net_rate        DECIMAL(12,2),
+    rate_gross      DECIMAL(12,2),
+    rate_net        DECIMAL(12,2),
     tariffs_data    JSONB DEFAULT '{}',
     valid_from      TIMESTAMP DEFAULT NOW(),
     last_verified_at TIMESTAMP DEFAULT NOW()
 );
 
+-- Migrate tables created before the gross_rate/net_rate → rate_gross/rate_net rename
+DO $$
+BEGIN
+    IF EXISTS (SELECT 1 FROM information_schema.columns
+               WHERE table_name = 'newbook_current_rates' AND column_name = 'gross_rate') THEN
+        ALTER TABLE newbook_current_rates RENAME COLUMN gross_rate TO rate_gross;
+        ALTER TABLE newbook_current_rates RENAME COLUMN net_rate TO rate_net;
+    END IF;
+END $$;
+
 CREATE INDEX IF NOT EXISTS idx_current_rates_date     ON newbook_current_rates(rate_date);
 CREATE INDEX IF NOT EXISTS idx_current_rates_category ON newbook_current_rates(category_id);
 CREATE INDEX IF NOT EXISTS idx_current_rates_tariffs  ON newbook_current_rates USING gin(tariffs_data);