feat(backend): implement REST API for races calendar

Express + TypeScript backend with PostgreSQL: CRUD endpoints for /races (GET list with year/month filters, GET by id, POST, PATCH, DELETE), health/readiness probes, SQL migration runner, seed script with upsert from CSV, camelCase/snake_case mapper, CORS, env validation, docker-compose, and API docs for frontend.

Made-with: Cursor

backend/migrations/001_create_races.sql

@@ -0,0 +1,16 @@
+CREATE TABLE IF NOT EXISTS races (
+  id               TEXT PRIMARY KEY,
+  race_date        DATE         NOT NULL,
+  title            TEXT         NOT NULL,
+  distance_km      NUMERIC(6,3) NOT NULL,
+  status           TEXT         CHECK (status IN ('planned', 'completed')),
+  official_url     TEXT,
+  start_time       TEXT,
+  cluster_schedule TEXT,
+  bib_pickup       TEXT,
+  bib_number       TEXT,
+  finish_time      TEXT,
+  notes            TEXT,
+  created_at       TIMESTAMPTZ  NOT NULL DEFAULT NOW(),
+  updated_at       TIMESTAMPTZ
+);