feat(docker): add multi-stage image and compose with persistent SQLite

Mount ./docker-data for WAL-capable SQLite storage, support DATABASE_PATH alias, and document compose secrets via .env.docker.example.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/config/env.validation.ts

@@ -19,6 +19,11 @@ export class EnvironmentVariables {
   @IsString()
   DB_PATH?: string
 
+  /** Alias for DB_PATH (e.g. Docker Compose). DB_PATH takes precedence when both are set. */
+  @IsOptional()
+  @IsString()
+  DATABASE_PATH?: string
+
   @IsOptional()
   @IsString()
   JWT_SECRET?: string
@@ -43,7 +48,7 @@ export function validateEnv(config: Record<string, unknown>): EnvironmentVariabl
     PORT: Number(config.PORT ?? 3001),
     HOST: (config.HOST as string | undefined) ?? '0.0.0.0',
     CORS_ORIGIN: (config.CORS_ORIGIN as string | undefined) ?? 'http://localhost:5173',
-    DB_PATH: config.DB_PATH as string | undefined,
+    DB_PATH: (config.DB_PATH ?? config.DATABASE_PATH) as string | undefined,
     JWT_SECRET: jwtSecret ?? 'gold-land-dev-secret-change-in-production',
   }