docs(readme): add getcodegraph.com waitlist banner

Advertise the upcoming hosted CodeGraph platform at the top of the README with a "Join the waitlist" CTA (early beta access) linking to getcodegraph.com, plus the button SVG asset.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -25,6 +25,14 @@
 [![Antigravity](https://img.shields.io/badge/Antigravity-supported-blueviolet.svg)](#supported-agents)
 [![Kiro](https://img.shields.io/badge/Kiro-supported-blueviolet.svg)](#supported-agents)
 
+<br>
+
+**The CodeGraph platform is coming** — for every PR, know exactly what to test, what could break, which flows are affected, and whether business logic is compromised.
+
+<a href="https://getcodegraph.com"><img alt="Join the waitlist for early beta access" src="https://raw.githubusercontent.com/colbymchenry/codegraph/main/assets/waitlist.svg" height="44"></a>
+
+<sub>Get <b>early beta access</b> to the hosted product · <a href="https://getcodegraph.com">getcodegraph.com</a></sub>
+
 </div>
 
 ## Get Started

assets/waitlist.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="192" height="44" viewBox="0 0 192 44" role="img" aria-label="Join the waitlist">
+  <rect x="0.5" y="0.5" width="191" height="43" fill="#7a201a" stroke="#5e1812"/>
+  <text x="96" y="27.5" text-anchor="middle"
+        font-family="-apple-system, BlinkMacSystemFont, 'Helvetica Neue', 'Segoe UI', Arial, sans-serif"
+        font-size="16" font-weight="600" fill="#f7f6f2">Join the waitlist<tspan dx="8">&#8594;</tspan></text>
+</svg>