feat(pgdb): add DATABASE_URI environment variable support

Add support for PostgreSQL connection URIs via DATABASE_URI env var.
When set, it takes precedence over config files and PoolOptions are
ignored (pool settings can be specified in URI query string).

database/pgdb/pool_test.go

@@ -1,6 +1,9 @@
 package pgdb
 
 import (
+	"context"
+	"os"
+	"strings"
 	"testing"
 	"time"
 
@@ -149,3 +152,63 @@ func TestCreatePoolConfigDefaults(t *testing.T) {
 		t.Errorf("Expected default Port=5432, got %d", poolCfg.ConnConfig.Port)
 	}
 }
+
+func TestOpenPoolWithDatabaseURI(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping integration test")
+	}
+
+	// This test requires a running PostgreSQL instance
+	uri := os.Getenv("TEST_DATABASE_URI")
+	if uri == "" {
+		t.Skip("TEST_DATABASE_URI not set")
+	}
+
+	ctx := context.Background()
+	t.Setenv("DATABASE_URI", uri)
+
+	pool, err := OpenPool(ctx, DefaultPoolOptions())
+	if err != nil {
+		t.Fatalf("OpenPool failed: %v", err)
+	}
+	defer pool.Close()
+
+	// Verify connection works
+	var result int
+	err = pool.QueryRow(ctx, "SELECT 1").Scan(&result)
+	if err != nil {
+		t.Fatalf("query failed: %v", err)
+	}
+	if result != 1 {
+		t.Errorf("expected 1, got %d", result)
+	}
+}
+
+func TestDatabaseURIPrecedence(t *testing.T) {
+	// Test that DATABASE_URI takes precedence over config files
+	// We use localhost with a port that's unlikely to have postgres running
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	// Set DATABASE_URI to a parseable URI pointing to a non-listening port
+	t.Setenv("DATABASE_URI", "postgres://testuser:testpass@127.0.0.1:59999/testdb?connect_timeout=1")
+
+	// Set config files to a nonexistent path - if this were used, we'd get
+	// "config file not found" error instead of connection refused
+	opts := DefaultPoolOptions()
+	opts.ConfigFiles = []string{"/nonexistent/path/database.yaml"}
+
+	_, err := OpenPool(ctx, opts)
+
+	// Should fail with connection error (not config file error)
+	// This proves DATABASE_URI was used instead of config files
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+
+	// The error should be about connection failure, not about missing config file
+	errStr := err.Error()
+	if strings.Contains(errStr, "config file") || strings.Contains(errStr, "no such file") {
+		t.Errorf("expected connection error, got config file error: %v", err)
+	}
+}