feat(channel): make message timeout configurable via channels_config.message_timeout_secs

Add configurable timeout for processing channel messages (LLM + tools).
Default: 300s (optimized for on-device LLMs like Ollama).
Can be overridden in config.toml:

[channels_config]
message_timeout_secs = 600

src/onboard/wizard.rs

@@ -2452,23 +2452,7 @@ fn setup_channels() -> Result<ChannelsConfig> {
     print_bullet("CLI is always available. Connect more channels now.");
     println!();
 
-    let mut config = ChannelsConfig {
-        cli: true,
-        telegram: None,
-        discord: None,
-        slack: None,
-        mattermost: None,
-        webhook: None,
-        imessage: None,
-        matrix: None,
-        signal: None,
-        whatsapp: None,
-        email: None,
-        irc: None,
-        lark: None,
-        dingtalk: None,
-        qq: None,
-    };
+    let mut config = ChannelsConfig::default();
 
     loop {
         let options = vec![