Migration system re-runs all migrations on every startup (no version tracking)

[TheRefreshCNFT]

Summary

nullboiler has no migration version tracking, causing all migrations to run on every startup. Migration 004's ALTER TABLE ADD COLUMN statements fail on any database that was previously initialized, crashing the process immediately.

Root Cause

1. store.zig migrate() runs all 4 migration SQL files unconditionally on every startup
2. Migration 004 contains ALTER TABLE ADD COLUMN statements for columns that already exist after the first successful run
3. state_json is already defined in 001_init.sql's CREATE TABLE runs — so migration 004 fails even on a fresh DB

Crash Output

info(store): migration 0+1 applied
info(store): migration 0+2 applied
info(store): migration 0+3 applied
error(store): migration 004 failed (rc=1): duplicate column name: state_json
error: MigrationFailed

Fix (PR #3)

PR #3 adds PRAGMA user_version tracking to store.zig:

• Read version on startup, only run migrations with number > current version
• Set version after each successful migration
• Migration SQL files unchanged — version gate makes them naturally idempotent

Upgrade Note for Existing Databases

Databases created before this fix have user_version=0 despite being fully migrated. One-time manual bump required:

import sqlite3
db = sqlite3.connect('nullboiler.db')
db.execute('PRAGMA user_version = 4')
db.commit()