docs(audience): move pixel Test mode section to sit with other init options

Group it with the other configuration sections (Consent Modes,
Auto-Tracked Events) instead of orphaning it after the operational
details (Cookies, CSP, Browser Support).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: bkbooth

packages/audience/pixel/README.md

@@ -106,6 +106,18 @@ document.head.appendChild(s);
 </script>
 ```
 
+## Test mode
+
+Set `"testMode": true` in the init options to mark every event with a
+top-level `test: true` flag. Useful for development, staging, or QA —
+events still flow through the production endpoint, but can be filtered
+out of production analytics downstream.
+
+```diff
+- w[i].push(["init",{"key":"YOUR_KEY","consent":"anonymous"}]);
++ w[i].push(["init",{"key":"YOUR_KEY","consent":"anonymous","testMode":true}]);
+```
+
 ## Cookies
 
 | Cookie | Lifetime | Purpose |
@@ -152,18 +164,6 @@ Note: the nonce covers the inline snippet only. The CDN-loaded script (`imtbl.js
 | Safari | 14+ |
 | Edge | 80+ |
 
-## Test mode
-
-Set `"testMode": true` in the init options to mark every event with a
-top-level `test: true` flag. Useful for development, staging, or QA —
-events still flow through the production endpoint, but can be filtered
-out of production analytics downstream.
-
-```diff
-- w[i].push(["init",{"key":"YOUR_KEY","consent":"anonymous"}]);
-+ w[i].push(["init",{"key":"YOUR_KEY","consent":"anonymous","testMode":true}]);
-```
-
 ## Documentation
 
 - [Tracking Pixel](https://docs.immutable.com/docs/products/audience/tracking-pixel) — this package (setup, consent modes, auto-tracked events)