feat(server): initial implementation

This commit captures the full server code accumulated across
several development sessions. It includes the following layers,
applied in roughly this order during development:

1. Base infrastructure
   - cmd/poc-server HTTP+WebSocket server, /health, /stats
   - internal/transport wire types (Envelope + all message types)
   - internal/catalog, internal/realtime, internal/stats
   - internal/storage/postgres with migrations 001-004
   - .env, .env.example, docker-compose, Dockerfile, scripts/

2. Swagger documentation
   - go get github.com/swaggo/http-swagger
   - swag init produces docs/docs.go
   - /swagger/index.html UI, /swagger/doc.json spec
   - annotations on health/stats/ws and catalog handlers

3. Races API
   - internal/races/{store,service,keyset,types}.go
   - migration 005_races.sql: finished_races, race_plans, race_queue
   - GET /api/races with keyset pagination, status filter
   - GET /api/races/upcoming
   - POST /api/races/queue/join, GET, DELETE
   - POST/GET /api/races/plans, DELETE /{id}
   - lobby.RaceMeta simplification (no host_id/host_name)

4. Races seeder
   - internal/races/seed with deterministic generator
   - --seed-races / --reset CLI flags in main.go
   - 30 finished + 5 live + 5 plans + 4 queue entries

5. Drivers and clans
   - internal/drivers, internal/clans (CRUD, validation)
   - migration 008_drivers_clans.sql
   - /api/clans and /api/drivers endpoints
   - 3-letter uppercase nickname/tag validation
   - lobby.DriverMeta: Nickname, AvatarURL, ClanID, ClanTag

6. Podium
   - internal/transport.RacePodiumEntry
   - lobby.SetDriverProfile for in-memory metadata sync
   - migration 007_podium.sql (podium JSONB column)
   - seeder populates top-3 per finished race

7. Live races persistence
   - migration 009_live_persistence.sql: live_races,
     live_race_drivers, lobby_drivers
   - internal/races/live_store.go: LiveStore with write-side
     mirror for lobby.Service mutations
   - Service.collectLive and Upcoming read from Postgres
   - main.go RestoreFromDB rehydrates lobby on startup

8. Unify live + finished into one races table
   - migration 010_unify_races.sql: rename finished_races to
     races, expand status CHECK, merge live rows
   - PgStore now hosts both write paths; LiveStore is a
     thin facade implementing lobby.Persistence
   - seeder resetAll drops only finished/cancelled rows and
     race_plans / race_queue / lobby_drivers

Each layer is consistent on its own; cross-layer changes are
visible in the file history. A future refactor may split this
commit into the per-stage boundaries listed above.

server/internal/storage/postgres/migrations/009_live_persistence.sql

@@ -0,0 +1,68 @@
+-- 009_live_persistence.sql — persistence for live races and lobby drivers.
+--
+-- The active race surface (lobby | countdown | racing) is now mirrored
+-- in Postgres. finished_races continues to be the canonical archive
+-- (no rename yet — it stays in the same shape and the next migration
+-- will unify the two under a single `races` table).
+--
+-- live_races
+--   One row per active race. Status is one of
+--   lobby | countdown | racing. The `podium` column is reserved for
+--   future use (we may eventually move finished_podium into this
+--   table as well).
+--
+-- live_race_drivers
+--   Many-to-many between live_races and drivers. The order column is
+--   the car's slot in the race (0..max_cars-1).
+--
+-- lobby_drivers
+--   Presence of a driver in the lobby: connected / idle / racing /
+--   offline and the current race if racing.
+
+CREATE TABLE IF NOT EXISTS live_races (
+    id              TEXT PRIMARY KEY,
+    name            TEXT NOT NULL,
+    track_id        TEXT NOT NULL,
+    max_cars        INT  NOT NULL,
+    laps            INT  NOT NULL,
+    time_limit_s    INT  NOT NULL,
+    status          TEXT NOT NULL DEFAULT 'lobby'
+                    CHECK (status IN ('lobby', 'countdown', 'racing', 'cancelled')),
+    created_ms      BIGINT NOT NULL,
+    started_ms      BIGINT NOT NULL DEFAULT 0,
+    finished_ms     BIGINT NOT NULL DEFAULT 0,
+    updated_ms      BIGINT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS live_races_status_idx
+    ON live_races (status, updated_ms DESC);
+CREATE INDEX IF NOT EXISTS live_races_track_idx
+    ON live_races (track_id);
+
+CREATE TABLE IF NOT EXISTS live_race_drivers (
+    race_id     TEXT NOT NULL REFERENCES live_races(id) ON DELETE CASCADE,
+    driver_id   TEXT NOT NULL,
+    slot        INT  NOT NULL DEFAULT 0,
+    joined_ms   BIGINT NOT NULL,
+    PRIMARY KEY (race_id, driver_id)
+);
+
+CREATE INDEX IF NOT EXISTS live_race_drivers_driver_idx
+    ON live_race_drivers (driver_id);
+
+CREATE TABLE IF NOT EXISTS lobby_drivers (
+    driver_id     TEXT PRIMARY KEY,
+    name          TEXT NOT NULL DEFAULT '',
+    nickname      TEXT NOT NULL DEFAULT '',
+    avatar_url    TEXT NOT NULL DEFAULT '',
+    clan_id       TEXT NOT NULL DEFAULT '',
+    clan_tag      TEXT NOT NULL DEFAULT '',
+    status        TEXT NOT NULL DEFAULT 'idle'
+                  CHECK (status IN ('idle', 'racing', 'offline')),
+    current_race_id TEXT NOT NULL DEFAULT '',
+    connected_ms  BIGINT NOT NULL,
+    last_seen_ms  BIGINT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS lobby_drivers_status_idx
+    ON lobby_drivers (status);