feat(03-01): add shared postgres pool and plugin migrations

Open one pgx stdlib *sql.DB, hand it to GORM, and run per-plugin
gormigrate sets with isolated history tables after an ICU pl-PL check.

Co-authored-by: Cursor <cursoragent@cursor.com>

cmd/summer/main_test.go

@@ -19,7 +19,7 @@ func TestToolCommandNames(t *testing.T) {
 	for _, c := range toolCommands() {
 		names = append(names, c.Name)
 	}
-	for _, want := range []string{"build", "make:plugin", "plugin:add", "dev"} {
+	for _, want := range []string{"build", "make:plugin", "plugin:add", "dev", "migrate", "migrate:rollback", "migrate:status"} {
 		if !slices.Contains(names, want) {
 			t.Fatalf("missing %s in %v", want, names)
 		}
@@ -61,7 +61,7 @@ func TestToolDoesNotImportExamplePlugins(t *testing.T) {
 				if err != nil {
 					t.Fatal(err)
 				}
-				if strings.Contains(path, "examples/hello") {
+				if strings.Contains(path, "examples/hello") || strings.Contains(path, "golem15/fonoteka") {
 					t.Fatalf("%s imports %s", name, path)
 				}
 			}