fix(tests): update database connection strings for CI

* Use dynamic host and port for Postgres in tests
* Add helper functions for test database host and port

tests/integration/testconfig_test.go

@@ -0,0 +1,26 @@
+package integration
+
+import (
+	"os"
+	"strconv"
+)
+
+// testDBHost and testDBPort let CI point the integration suite at a
+// dynamically-assigned Postgres (TEST_DB_HOST/TEST_DB_PORT), avoiding a fixed
+// host port that can collide with other jobs on a shared runner. Local dev
+// keeps working unset, defaulting to the docker-compose test stack.
+func testDBHost() string {
+	if h := os.Getenv("TEST_DB_HOST"); h != "" {
+		return h
+	}
+	return "127.0.0.1"
+}
+
+func testDBPort() int {
+	if p := os.Getenv("TEST_DB_PORT"); p != "" {
+		if n, err := strconv.Atoi(p); err == nil {
+			return n
+		}
+	}
+	return 5433
+}