[Precursor] Precursor Changelog Entry for Launch 13 July (#31914)

* [Challenges] Add Precursor changelog launch entry

Add the Cloudflare Challenges changelog post for Precursor session-based detection, including links to the launch blog and Precursor docs. Include an animated dashboard walkthrough asset for enablement context.

* Update src/content/changelog/cloudflare-challenges/2026-07-13-precursor-session-based-detection.mdx

Co-authored-by: Miguel de Moura <9093796+migueldemoura@users.noreply.github.com>

---------

Co-authored-by: Miguel de Moura <9093796+migueldemoura@users.noreply.github.com>

Author: marinaelmore

public/images/precursor/enabling_precursor.gif

@@ -0,0 +1,26 @@
+---
+title: Precursor introduces session-based bot detection
+description: Precursor brings continuous, session-based behavioral detection to Cloudflare Challenges.
+date: 2026-07-13
+---
+
+Precursor is rolling out to all customers starting today. Precursor is client-side JavaScript that enables session-based bot detection.
+
+You can [read the announcement blog](https://blog.cloudflare.com/introducing-precursor) for background on why we built Precursor and how session-level behavioral detection works.
+
+With Precursor enabled, Cloudflare can:
+
+- Continuously evaluate behavioral signals across a session
+- Re-validate challenge clearance as behavior changes
+- Update bot scores with session context
+- Provide client-side visibility where none previously existed
+
+It integrates with existing protections, including Security Rules, and can be enabled directly from the Cloudflare dashboard with configurable modes to balance security and user experience.
+
+<img
+	src="/images/precursor/enabling_precursor.gif"
+	alt="Animated walkthrough of enabling Precursor in the Cloudflare dashboard"
+	style="border:1px solid #e5e7eb;border-radius:6px;display:block;margin:16px 0;"
+/>
+
+To learn more, refer to the [Precursor documentation](/cloudflare-challenges/precursor/).