New content (guides/refs/updates to existing for LLM content gaps)

gatsby-config.js

@@ -551,6 +551,10 @@ module.exports = {
             title: "Hello, World!",
             path: "guides/getting_started/hello-world.md",
           },
+          {
+            title: "Project Anatomy",
+            path: "guides/getting_started/addon-project-anatomy.md",
+          },
           {
             title: "Code Playground",
             path: "guides/getting_started/code_playground.md",
@@ -778,18 +782,40 @@ module.exports = {
           },
           {
             title: "Platform Concepts",
-            path: "guides/learn/platform_concepts/context.md",
+            path: "guides/learn/platform_concepts/architecture.md",
             pages: [
               {
-                title: "Add-on Iframe Context",
-                path: "guides/learn/platform_concepts/context.md",
+                title: "Add-on Architecture",
+                path: "guides/learn/platform_concepts/architecture.md",
               },
+              {
+                title: "iframe Runtime Context & Security",
+                path: "guides/learn/platform_concepts/context.md",
+              },              
               {
                 title: "The Document API",
                 path: "guides/learn/platform_concepts/document-api.md",
               },
             ],
           },
+          {
+            title: "SDK Fundamentals",
+            path: "guides/learn/fundamentals/terminology.md",
+            pages: [
+              {
+                title: "Terminology",
+                path: "guides/learn/fundamentals/terminology.md",
+              },
+              {
+                title: "Using Add-on UI SDK Constants",
+                path: "guides/learn/fundamentals/ui-sdk-constants.md",
+              },
+              {
+                title: "Using Document Sandbox Constants",
+                path: "guides/learn/fundamentals/document-sandbox-constants.md",
+              }              
+            ],
+          },
           {
             title: "Sample add-ons",
             path: "guides/learn/samples.md",