BRIDGE-3: Shop ← Freight Watermarks (River Stage 1 → landed cost)

Connect River Pipeline Stage 1 (Freight) output to Shop /landed-cost endpoint. River already has watermarks for: - freight_fbx: Freightos Baltic Index (ocean container rates) - freight_scfi: Shanghai Containerized Freight Index - freight_dat: DAT (US trucking spot rates) - freight_tac: TransRussiaAgency Container (rail rates) - freight_wci: World Container Index Currently these watermarks are empty (pipeline stages exist but don't execute). Implementation: 1. Activate River freight stage — scrape/API-pull latest indices 2. Store in new table: freight_indices (route, mode, rate_usd, index_name, fetched_at) 3. Shop /landed-cost reads latest rates: get_freight_rate(origin, dest, mode) 4. Fallback: if no fresh data (<7 days), use Freightos CO2 API (already integrated) This makes landed cost calculations use REAL market rates, not estimates. Enterprise customers ($5K/mo) need this for accurate procurement planning. Output: River freight executor + freight_indices table + Shop integration Blocked by: Shop service (89c53d32)