feat: add environment labels (local/dev/stage/prod) for connections

Visual badges help distinguish environments across the UI to prevent
running dangerous queries on production. Environment color takes
priority over custom connection color for the toolbar border.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types/index.ts

@@ -8,6 +8,7 @@ export interface ConnectionConfig {
   database: string;
   ssl_mode?: string;
   color?: string;
+  environment?: string;
 }
 
 export interface QueryResult {