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>

internal/build/build_test.go

@@ -94,6 +94,9 @@ func TestGenerateStableQuotedImportsInManifestOrder(t *testing.T) {
 	if !bytes.Contains(mainSrc, []byte(`bonfire.NewRoot("hello"`)) {
 		t.Fatalf("main does not use manifest binary:\n%s", mainSrc)
 	}
+	if !bytes.Contains(mainSrc, []byte("lagoon.RuntimeCommands")) {
+		t.Fatalf("main does not register lagoon runtime commands:\n%s", mainSrc)
+	}
 	if bytes.Contains(mainSrc, []byte("examples/hello")) {
 		t.Fatal("generated main hard-codes examples/hello")
 	}