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

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Embedded auto-migrating database schema system (`server/migrations/`): the server binary now contains all SQL schemas and runs migrations automatically on startup — no more `pg_restore`, manual patch ordering, or external `schemas/` directory needed
 - Setup wizard: web-based first-run configuration at `http://localhost:8080` when `config.json` is missing — guides users through database connection, schema initialization, and server settings
 - CI: Coverage threshold enforcement — fails build if total coverage drops below 50%
 - CI: Release workflow that automatically builds and uploads Linux/Windows binaries to GitHub Releases on tag push
@@ -25,6 +26,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Schema management consolidated: replaced 4 independent code paths (Docker shell script, setup wizard, test helpers, manual psql) with a single embedded migration runner
+- Setup wizard simplified: 3 schema checkboxes replaced with single "Apply database schema" checkbox
+- Docker simplified: removed schema volume mounts and init script — the server binary handles everything
+- Test helpers simplified: `ApplyTestSchema` now uses the migration runner instead of `pg_restore` + manual patch application
 - Updated minimum Go version requirement from 1.23 to 1.25
 - Improved config handling
 - Refactored logout flow to save all data before cleanup (prevents data loss race conditions)