docs: align dev setup docs with current server config

## Changes
- Replace stale QUEUE_TYPE env var (superSimpleQueue/lessSimpleQueue) with QUEUE_MODE (primary/worker) to match server/src/config/envValidation.ts
- Mark ORIGIN, TOKEN_TTL and LOG_LEVEL as optional with their defaults; note that only CLIENT_HOST, JWT_SECRET and DB_CONNECTION_STRING are strictly required
- Note that CLIENT_HOST must be a full URL (enforced by env validation)
- Remove Redis port 6379 from the port-conflict troubleshooting list; the server has no Redis dependency
- Point CLAUDE.md at CONTRIBUTING.md as the setup source of truth

## Why
A contributor followed the setup docs and hit references to files and env vars that no longer exist after the repo reorg. This brings the contributor docs in line with the actual dev workflow.

CLAUDE.md

@@ -51,6 +51,7 @@ TOKEN_TTL="99d"
 ORIGIN="localhost"
 LOG_LEVEL="debug"
 ```
+Only `CLIENT_HOST` (must be a full URL), `JWT_SECRET`, and `DB_CONNECTION_STRING` are strictly required; the rest have defaults (see `server/src/config/envValidation.ts`). Setup source of truth: CONTRIBUTING.md.
 
 ### Client `.env`
 ```env

CONTRIBUTING.md

@@ -124,10 +124,12 @@ LOG_LEVEL="debug"
 - `CLIENT_HOST`: Frontend URL (default: http://localhost:5173)
 - `JWT_SECRET`: Secret key for JWT tokens (change to something secure)
 - `DB_CONNECTION_STRING`: MongoDB connection URL
-- `ORIGIN`: Origin for CORS purposes
-- `TOKEN_TTL`: Token time to live (in vercel/ms format)
-- `LOG_LEVEL`: Debug level (debug, info, warn, error)
-- `QUEUE_TYPE`: Job queue implementation (`superSimpleQueue` or `lessSimpleQueue`, optional, default: `superSimpleQueue`)
+- `ORIGIN`: Origin for CORS purposes (optional)
+- `TOKEN_TTL`: Token time to live in vercel/ms format (optional, default: `99d`)
+- `LOG_LEVEL`: Debug level: debug, info, warn, error (optional, default: `debug`)
+- `QUEUE_MODE`: Queue mode, `primary` or `worker` (optional, default: `primary`)
+
+Only `CLIENT_HOST`, `JWT_SECRET`, and `DB_CONNECTION_STRING` are strictly required. Note that `CLIENT_HOST` must be a full URL.
 
 Start the backend server:
 
@@ -203,7 +205,7 @@ docker rm uptime_database_mongo
 
 **Port already in use:**
 
-- Check if another service is using ports 5173, 52345, 27017, or 6379
+- Check if another service is using ports 5173, 52345, or 27017
 - Stop the conflicting service or change the port in `.env` files
 
 **MongoDB connection issues:**