feat: add BullMQ job queue with admin monitoring UI

- Add BullMQ to backend; mail jobs (verification, password reset) now enqueued instead of sent inline
- Mail worker processes jobs with 3-attempt exponential backoff retry
- Admin GraphQL resolvers: adminQueues, adminQueueJobs, adminRetryJob, adminRemoveJob, adminPauseQueue, adminResumeQueue
- Admin frontend page at /admin/queues: queue cards with counts, job table with status filter, retry/remove/pause actions

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

packages/backend/src/graphql/resolvers/auth.ts

@@ -9,7 +9,7 @@ interface ReplyLike {
 }
 import { hash, verify as verifyArgon } from "../../lib/argon";
 import { setSession, deleteSession } from "../../lib/auth";
-import { sendVerification, sendPasswordReset } from "../../lib/email";
+import { enqueueVerification, enqueuePasswordReset } from "../../lib/email";
 import { slugify } from "../../lib/slugify";
 import { nanoid } from "nanoid";
 
@@ -131,9 +131,9 @@ builder.mutationField("register", (t) =>
       });
 
       try {
-        await sendVerification(args.email, verifyToken);
+        await enqueueVerification(args.email, verifyToken);
       } catch (e) {
-        console.warn("Failed to send verification email:", (e as Error).message);
+        console.warn("Failed to enqueue verification email:", (e as Error).message);
       }
       return true;
     },
@@ -190,9 +190,9 @@ builder.mutationField("requestPasswordReset", (t) =>
         .where(eq(users.id, user[0].id));
 
       try {
-        await sendPasswordReset(args.email, token);
+        await enqueuePasswordReset(args.email, token);
       } catch (e) {
-        console.warn("Failed to send password reset email:", (e as Error).message);
+        console.warn("Failed to enqueue password reset email:", (e as Error).message);
       }
       return true;
     },