landing: add modular architecture diagram

landing/index.html

@@ -84,6 +84,26 @@ flowchart TB
                 <h2 class="section-title" id="architecture-heading">Architecture Overview</h2>
                 <pre class="mermaid">
 ---
+config:
+  layout: fixed
+  theme: base
+  themeVariables:
+    primaryColor: '#e94a39'
+    primaryBorderColor: '#e94a39'
+    lineColor: '#e94a39'
+  look: classic
+---
+graph TD
+    core(seedpass.core)
+    cli(CLI/TUI)
+    gui(BeeWare GUI)
+    ext(Browser extension)
+    cli --> core
+    gui --> core
+    ext --> core
+                </pre>
+                <pre class="mermaid">
+---
 config:
   layout: fixed
   theme: base