docs: finalize onboarding option heading normalization (#22547)

* docs(channels): promote Signal option setups to onboarding sections

* docs(channels): rename Microsoft Teams minimal setup section

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

docs/channels/msteams.md

@@ -236,7 +236,7 @@ This is often easier than hand-editing JSON manifests.
 2. Find the bot in Teams and send a DM
 3. Check gateway logs for incoming activity
 
-## Setup (minimal)
+## Onboarding (minimal)
 
 
 1. **Install the Microsoft Teams plugin**

docs/channels/signal.md

@@ -76,7 +76,7 @@ Disable with:
 - If you run the bot on **your personal Signal account**, it will ignore your own messages (loop protection).
 - For "I text the bot and it replies," use a **separate bot number**.
 
-## Setup (option A): link existing Signal account (QR)
+## Onboarding (option A): link existing Signal account (QR)
 
 1. Install `signal-cli` (JVM or native build).
 2. Link a bot account:
@@ -101,7 +101,7 @@ Example:
 
 Multi-account support: use `channels.signal.accounts` with per-account config and optional `name`. See [`gateway/configuration`](/gateway/configuration#telegramaccounts--discordaccounts--slackaccounts--signalaccounts--imessageaccounts) for the shared pattern.
 
-## Setup (option B): register dedicated bot number (SMS, Linux)
+## Onboarding (option B): register dedicated bot number (SMS, Linux)
 
 Use this when you want a dedicated bot number instead of linking an existing Signal app account.
 

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)