Add repository and boot-path tests for Feature 02 review

Addresses feature-review findings F1 and F2 on PR #14.

F1: internal/store/repository_test.go inserts, reads back and updates a
row in week_plans, plan_days, suggestions, shopping_lists,
shopping_groups and shopping_items against a migrated temp database,
using raw SQL and seeding foreign-key parents.

F2: TestMigrateReopenSameDataDirIsNoOp reopens the same data directory
and proves Migrate leaves schema_migrations and the schema unchanged.
cmd/server extracts the open+migrate boot step into openStore over an
injectable bootMigrations set; tests prove a broken migration makes
openStore and run return the error before listening.

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

cmd/server/main.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io/fs"
 	"log/slog"
 	"net/http"
 	"os"
@@ -40,7 +41,7 @@ func run(cfg config.Config, logger *slog.Logger) error {
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
 
-	db, err := store.Open(ctx, cfg.DataDir)
+	db, err := openStore(ctx, cfg.DataDir)
 	if err != nil {
 		return err
 	}
@@ -49,9 +50,6 @@ func run(cfg config.Config, logger *slog.Logger) error {
 			logger.Error("close database", "error", err)
 		}
 	}()
-	if err := store.Migrate(ctx, db.Writer, migrations.FS); err != nil {
-		return err
-	}
 
 	router, err := server.NewRouter(logger, version, frontend.Assets())
 	if err != nil {
@@ -88,6 +86,23 @@ func run(cfg config.Config, logger *slog.Logger) error {
 	return nil
 }
 
+// bootMigrations is the migration set applied at boot. Tests replace it to
+// prove a failing migration stops the boot.
+var bootMigrations fs.FS = migrations.FS
+
+// openStore opens the database in dataDir and applies bootMigrations. On a
+// migration failure it closes the database and returns the error.
+func openStore(ctx context.Context, dataDir string) (*store.Store, error) {
+	db, err := store.Open(ctx, dataDir)
+	if err != nil {
+		return nil, err
+	}
+	if err := store.Migrate(ctx, db.Writer, bootMigrations); err != nil {
+		return nil, errors.Join(err, db.Close())
+	}
+	return db, nil
+}
+
 // logListening logs the startup line. Only the public URL's origin is logged
 // so no credential-bearing URL component can reach the log.
 func logListening(logger *slog.Logger, cfg config.Config) {