docs: Replace agent-and-renderer.png by a Mermaid diagram. (#1464)

* docs: Replace agent-and-renderer.png by a Mermaid diagram.
* docs: Add Glossary menu entry under Concepts

Author: ditman

docs/assets/agent-and-renderer.png

@@ -14,7 +14,18 @@ The A2UI protocol enables conversation between **agent** and **renderer**:
     - Receives **user input**, communicated by renderer
     - Updates **data** to show in UI
 
-![agent and renderer](assets/agent-and-renderer.png)
+```mermaid
+sequenceDiagram
+    participant Renderer as A2UI Renderer
+    participant Agent as A2UI Agent
+
+    Renderer->>Agent: Catalog & instructions
+
+    loop Agentic flow
+        Agent->>Renderer: Data + UI Updates. Function calls.
+        Renderer->>Agent: User input
+    end
+```
 
 While the protocol is designed for **AI-empowered agents**, it can work with deterministic agents as well. For example, an agent may return a pre-canned A2UI UI.
 

docs/glossary.md docs/concepts/glossary.mddocs/glossary.md renamed to docs/concepts/glossary.md

@@ -2,7 +2,7 @@
 
 This section explains the fundamental architecture of A2UI. Understanding these concepts will help you build effective agent-driven interfaces.
 
-See [Glossary](../glossary.md) for short definitions of key terms.
+See [Glossary](glossary.md) for short definitions of key terms.
 
 ## The Big Picture
 

docs/concepts/overview.md

@@ -42,6 +42,7 @@ nav:
   - A2UI Composer ⭐: composer.md
   - Concepts:
       - Overview: concepts/overview.md
+      - Glossary: concepts/glossary.md
       - Data Flow: concepts/data-flow.md
       - Components & Structure: concepts/components.md
       - Data Binding: concepts/data-binding.md