docs: add v0.42.0 changelog entry with release images

Add changelog entry for BrowserOS v0.42.0 featuring SOUL.md, vertical tabs,
long-term memory, and Chromium 146 update. Include screenshots from the
GitHub release.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/changelog.mdx

@@ -7,6 +7,24 @@ All notable changes to BrowserOS are documented here. For the full release histo
 
 ---
 
+## v0.42.0
+<sub>March 9, 2026</sub>
+
+- **SOUL.md** — Your assistant now has a soul. Tell it how you like to communicate, set boundaries, shape its personality — and it adapts on its own over time. The more you use it, the more it feels like *your* assistant. [Read more →](/features/soul)
+- **Vertical tabs** — One of the most requested features is here. BrowserOS now ships with vertical tabs by default. More screen space, better tab management, and a cleaner layout out of the box. Prefer horizontal? You can switch back anytime in settings. [Read more →](/features/vertical-tabs)
+- **Long-term memory** — Your assistant finally remembers you. Your name, your projects, what you talked about last week — it carries context across every conversation so you never have to repeat yourself. All stored locally on your machine. [Read more →](/features/memory)
+- **Chromium 146** — Updated to the latest Chromium release with all recent upstream fixes and security patches
+
+<Frame>
+  <img src="/images/changelog/0.42.0/soul-memory.png" alt="BrowserOS v0.42.0 SOUL.md feature for agent personalization" />
+</Frame>
+
+<Frame>
+  <img src="/images/changelog/0.42.0/vertical-tabs.png" alt="BrowserOS v0.42.0 vertical tabs toggle in settings" />
+</Frame>
+
+---
+
 ## v0.41.0
 <sub>March 4, 2026</sub>