fix(docs): depend on nanobot-ai, not the unrelated nanobot package

The PyPI package `nanobot` is a different project ("Minimalist robot
navigation framework"), not this one. This project publishes as
`nanobot-ai` (see pyproject.toml). Following the guide as-written would
pull down the wrong package — flagged by vansatchen in #3188.

Same toml block as the build-backend fix, one-word change.

Made-with: Cursor

docs/CHANNEL_PLUGIN_GUIDE.md

@@ -135,7 +135,7 @@ class WebhookChannel(BaseChannel):
 [project]
 name = "nanobot-channel-webhook"
 version = "0.1.0"
-dependencies = ["nanobot", "aiohttp"]
+dependencies = ["nanobot-ai", "aiohttp"]
 
 [project.entry-points."nanobot.channels"]
 webhook = "nanobot_channel_webhook:WebhookChannel"