feat(config): use REDIS_URL for redis

docs/setup-guide.md

@@ -11,6 +11,7 @@
 ```bash
 cp .env.example .env
 # set TELEGRAM_BOT_TOKEN in .env
+# REDIS_URL is overridden to redis://redis:6379/0 by docker compose
 docker compose up --build
 ```
 
@@ -27,6 +28,7 @@ Run bot:
 ```bash
 cp .env.example .env
 # export TELEGRAM_BOT_TOKEN or source .env with your shell workflow
+# REDIS_URL defaults to redis://localhost:6379/0
 go run ./cmd/openai-status-bot
 ```
 
@@ -34,7 +36,7 @@ go run ./cmd/openai-status-bot
 
 ```bash
 go test ./...
-go build ./cmd/openai-status-bot
+go build -o /tmp/openai-status-bot ./cmd/openai-status-bot
 ```
 
 Then send `/start` to the Telegram bot and run `/status`. If the same token was previously used by a webhook deployment, startup clears that webhook before long polling begins.

docs/system-architecture.md

@@ -38,7 +38,7 @@ Subscriber set members are `chatID` or `chatID:threadID`. Missing settings defau
 
 ## Runtime
 
-The service uses Telegram `getUpdates`, so it does not need a public webhook URL. On startup it calls `deleteWebhook` before long polling, which allows migration from a webhook-based deployment using the same bot token. Docker Compose starts Redis and the bot.
+The service uses Telegram `getUpdates`, so it does not need a public webhook URL. On startup it calls `deleteWebhook` before long polling, which allows migration from a webhook-based deployment using the same bot token. Redis is configured with `REDIS_URL`. Docker Compose starts Redis and the bot.
 
 ## Failure Behavior