docs(channels): standardize onboarding option headings for Zalo and Twitch

docs/channels/twitch.md

@@ -67,7 +67,7 @@ Minimal config:
 - Each account maps to an isolated session key `agent:<agentId>:twitch:<accountName>`.
 - `username` is the bot's account (who authenticates), `channel` is which chat room to join.
 
-## Setup (detailed, recommended)
+## Onboarding (detailed, recommended)
 
 ### Generate credentials
 

docs/channels/zalo.md

@@ -53,7 +53,7 @@ It is a good fit for support or notifications where you want deterministic routi
 - DMs share the agent's main session.
 - Groups are not yet supported (Zalo docs state "coming soon").
 
-## Setup (quick path)
+## Onboarding (quick path)
 
 ### 1) Create a bot token (Zalo Bot Platform)