feat(db): add embedded auto-migrating schema system

Replace 4 independent schema management code paths (Docker shell
script, setup wizard pg_restore, test helpers, manual psql) with a
single migration runner embedded in the server binary.

The new server/migrations/ package uses Go embed to bundle all SQL
schemas. On startup, Migrate() creates a schema_version tracking
table, detects existing databases (auto-marks baseline as applied),
and runs pending migrations in transactions.

Key changes:
- Consolidated init.sql + 9.2-update + 33 patches into 0001_init.sql
- Setup wizard simplified to single "Apply schema" checkbox
- Test helpers use migrations.Migrate() instead of pg_restore
- Docker no longer needs schema volume mounts or init script
- Seed data (shops, events, gacha) embedded and applied via API
- Future migrations just add 0002_*.sql files — no manual steps

docker/docker-compose.yml

@@ -14,8 +14,6 @@ services:
       - "5432:5432"
     volumes:
       - ./db-data/:/var/lib/postgresql/
-      - ../schemas/:/schemas/
-      - ./init/setup.sh:/docker-entrypoint-initdb.d/setup.sh
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U postgres"]
       interval: 5s

docker/init/setup.sh

@@ -1,27 +0,0 @@
-#!/bin/bash
-set -e
-
-echo "INIT: Restoring database schema..."
-pg_restore --username="$POSTGRES_USER" --dbname="$POSTGRES_DB" --no-owner --no-acl --verbose /schemas/init.sql || {
-  echo "WARN: pg_restore exited with errors (this is expected if the database already has objects)"
-}
-
-echo "Updating!"
-for file in /schemas/update-schema/*; do
-  echo "  Applying $file"
-  psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" -1 -f "$file"
-done
-
-echo "Patching!"
-for file in /schemas/patch-schema/*; do
-  [ -f "$file" ] || continue
-  echo "  Applying $file"
-  psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" -1 -f "$file"
-done
-
-echo "Loading bundled data (shops, events, gacha)..."
-for file in /schemas/bundled-schema/*; do
-  [ -f "$file" ] || continue
-  echo "  Applying $file"
-  psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" -1 -f "$file"
-done