fix(db): numbered migrations that run once and fail loudly (FLAW-13)

schema_migrations records every applied step; the former migrate() is
step 3, the baseline that builds the v0.4.1 schema and repairs older
databases. Columns are only added when missing, so every other error now
stops the start with a clear message instead of being swallowed, and the
cleanup statements no longer run on each start. migrations/001_init.sql
was never read and is gone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/migrations_test.go

@@ -0,0 +1,45 @@
+package storage
+
+import (
+	"errors"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestMigrationsRunOnceAndRepairOldDatabases(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "migrate.db")
+	store, err := NewStore(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var n int
+	_ = store.db.QueryRow(`SELECT COUNT(*) FROM schema_migrations`).Scan(&n)
+	if n != len(migrations) {
+		t.Fatalf("expected %d recorded migrations, got %d", len(migrations), n)
+	}
+
+	// A database from before the migration table, missing a later column
+	if _, err := store.db.Exec(`ALTER TABLE thoughts DROP COLUMN alarm_failures`); err != nil {
+		t.Fatal(err)
+	}
+	_, _ = store.db.Exec(`DROP TABLE schema_migrations`)
+	_ = store.Close()
+
+	store, err = NewStore(path)
+	if err != nil {
+		t.Fatalf("reopen: %v", err)
+	}
+	if ok, _ := store.columnExists("thoughts", "alarm_failures"); !ok {
+		t.Fatal("baseline must add missing columns to older databases")
+	}
+
+	// A failing step stops the start with its error and is not recorded
+	saved := migrations
+	defer func() { migrations = saved }()
+	migrations = append(append([]migration{}, saved...), migration{999, "kaputt", func(*Store) error { return errors.New("boom") }})
+	_ = store.Close()
+	if _, err := NewStore(path); err == nil || !strings.Contains(err.Error(), "Migration 999") {
+		t.Fatalf("failing migration must abort the start, got %v", err)
+	}
+}