feat: Implement lazy hub expansion depth limiting with transfer depth limit of 5 (Task 14)

db/migrations/20260816_create_transfer_rules_table.up.sql

@@ -0,0 +1,24 @@
+-- Migration: Create transfer_rules table for MCT (Minimum Connection Time) values
+-- This table stores minimum connection time rules based on transfer context:
+--   - airport_internal/through: 30 min (within same airport, through transfer)
+--   - airport_internal/separate: 60 min (within same airport, separate transfers)
+--   - station_internal: 30 min (between stations in same city)
+--   - airport_to_city/small: 60 min (airport to small city)
+--   - airport_to_city/million_plus: 90 min (airport to million+ city)
+
+CREATE TABLE IF NOT EXISTS transfer_rules (
+    id SERIAL PRIMARY KEY,
+    rule_key VARCHAR(50) NOT NULL UNIQUE,
+    min_transfer_time_minutes INTEGER NOT NULL,
+    description TEXT,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Insert default MCT values
+INSERT INTO transfer_rules (rule_key, min_transfer_time_minutes, description) VALUES
+    ('airport_internal_through', 30, 'Minimum transfer time for internal connections at the same airport (through transfer)'),
+    ('airport_internal_separate', 60, 'Minimum transfer time for internal connections at the same airport (separate transfers)'),
+    ('station_internal', 30, 'Minimum transfer time between stations in the same city'),
+    ('airport_to_city_small', 60, 'Minimum transfer time from airport to small city'),
+    ('airport_to_city_million_plus', 90, 'Minimum transfer time from airport to million-plus city');