refactor: split monolith into 3 microservices (frontend, backend, discord-gateway)

- Extract services into services/{frontend,backend,discord-gateway}
- Create packages/shared/ for shared logger, errors, utils, types
- Setup Modular MVC pattern in backend (controller→service→repository)
- Setup event-driven architecture in discord-gateway with Redis pub/sub
- Move Docker files to infra/docker/ with per-service Dockerfiles
- Update docker-compose.yml to use Traefik-only routing (no port exposes)
- Update GitHub Actions deploy workflow for multi-service matrix build
- Fix all import paths and resolve type errors across all services
- All 3 services pass tsc --noEmit clean

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/discord-gateway/src/shared/utils/retry.ts

@@ -0,0 +1,42 @@
+import pRetry from "p-retry";
+import type { CustomLogger } from "../../shared/logger/logger.js";
+
+export interface RetryOptions {
+  retries?: number;
+  minTimeout?: number;
+  maxTimeout?: number;
+  factor?: number;
+  logger?: CustomLogger;
+}
+
+export async function retryWithBackoff<T>(
+  fn: () => Promise<T>,
+  options: RetryOptions = {},
+): Promise<T> {
+  const {
+    retries = 3,
+    minTimeout = 1000,
+    maxTimeout = 30000,
+    factor = 2,
+    logger,
+  } = options;
+
+  return pRetry(fn, {
+    retries,
+    minTimeout,
+    maxTimeout,
+    factor,
+    onFailedAttempt: (error) => {
+      if (logger) {
+        logger.warn(
+          {
+            attempt: error.attemptNumber,
+            retriesLeft: error.retriesLeft,
+            error: error.error,
+          },
+          "Retry attempt",
+        );
+      }
+    },
+  });
+}