fix(channels): complete dependency manifest migration (#4995)

* fix(channels): complete dependency manifest migration

* docs(docker): clarify custom uid dependency installs

* fix(channels): keep dependency preinstall internal

* refactor(channels): move dependency installer to scripts

* fix(docker): limit runtime write access

docs/chat-apps.md

@@ -46,8 +46,8 @@ The sections below explain what each chat platform requires and provide manual c
 
 > [!NOTE]
 > If you are upgrading from a version where chat app SDKs were installed by default,
-> install the channel extra in the same Python environment before enabling or
-> restarting that channel:
+> enable the channel in the same Python environment so nanobot installs its
+> manifest-declared dependencies:
 >
 > ```bash
 > nanobot plugins enable <channel>
@@ -185,7 +185,7 @@ Uses **Socket.IO WebSocket** by default, with HTTP polling fallback.
 nanobot plugins enable mochat
 ```
 
-Without this extra, Mochat still works through HTTP polling.
+Without these dependencies, Mochat still works through HTTP polling.
 
 **1. Ask nanobot to set up Mochat for you**