fix: make postgresql actually usable (4 critical bugs)

- CORS whitelist only allowed origin localhost:5173; browsers send Origin
  on same-origin POST too, so every deployment on any other port/origin
  got empty 403 on ALL POST/PUT/DELETE (curl tests masked it) - now
  echoes any origin (bearer-token auth, no cookie CSRF surface)
- connection_tester pg DSN had a literal *** password placeholder - pg
  connection test and query path could never authenticate
- instance detail endpoints (databases/tables/db-schema/table-detail)
  ran MySQL SHOW statements against pg - added pg branches
  (pg_database/pg_class/information_schema/pg_indexes, search_path
  semantics, PRI detection); schema filter uses non-system schemas
- frontend normalizeDbType missed the literal 'postgresql' value so pg
  instances were treated as mysql (backtick quoting, no column hints);
  genSql no longer emits db.table prefix for pg (schema semantics)
- also: query page footer warnings condensed to a single line per db type

verified live: mysql table tree/context menu/preview-execute; pg table
tree/columns/PK, double-click preview with masking working (email/phone
masked), query history persisted

backend/internal/handler/connection_tester.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"fmt"
 	"math"
+	"net/url"
 	"strconv"
 	"strings"
 	"time"
@@ -116,8 +117,8 @@ func testPostgreSQL(ctx context.Context, host string, port int, user, pass, dbna
 	if dbname == "" {
 		dbname = "postgres"
 	}
-	dsn := fmt.Sprintf("postgres://%s:***@%s:%d/%s?sslmode=disable&connect_timeout=10",
-		user, host, port, dbname)
+	dsn := fmt.Sprintf("postgres://%s:%s@%s:%d/%s?sslmode=disable&connect_timeout=10",
+		url.PathEscape(user), url.QueryEscape(pass), host, port, url.PathEscape(dbname))
 	db, err := sql.Open("pgx", dsn)
 	if err != nil {
 		return false, fmt.Sprintf("Connection failed: %v", err)
@@ -549,8 +550,8 @@ func getDBConnection(instance *model.Instance, dbName string) (*sql.DB, error) {
 		if dbName == "" {
 			dbName = "postgres"
 		}
-		dsn := fmt.Sprintf("postgres://%s:***@%s:%d/%s?sslmode=disable&connect_timeout=10",
-			instance.Username, instance.Host, instance.Port, dbName)
+		dsn := fmt.Sprintf("postgres://%s:%s@%s:%d/%s?sslmode=disable&connect_timeout=10",
+			url.PathEscape(instance.Username), url.QueryEscape(password), instance.Host, instance.Port, url.PathEscape(dbName))
 		return sql.Open("pgx", dsn)
 	default:
 		return nil, fmt.Errorf("unsupported database type: %s", instance.DBType)