Add developer guides section and update docs navigation

Added new guides for Getting Started, Installation, and Project Structure under a new 'guides' section. Updated the main documentation index to include a 'Getting Started' card and modified meta.json files to register the new guides section and its pages.

Author: hotlong

content/docs/guides/getting-started.mdx

@@ -3,8 +3,6 @@ title: Getting Started
 description: Build your first ObjectStack application in 5 minutes.
 ---
 
-import { Step, Steps } from 'fumadocs-ui/components/steps';
-
 ObjectStack is a protocol, but `@objectstack/spec` is the reference implementation library that provides the Zod schemas and strict types to build valid metadata.
 
 <Steps>

content/docs/guides/project-structure.mdx

@@ -3,11 +3,9 @@ title: Project Structure
 description: Recommended directory layout for ObjectStack projects.
 ---
 
-import { File, Folder } from 'lucide-react';
-
 To keep your metadata organized, we recommend the following folder structure ("The Domain Pattern").
 
-<Files>
+<FileTree>
   <Folder name="src" defaultOpen>
     <Folder name="domains" defaultOpen>
       <Folder name="crm" defaultOpen>
@@ -32,7 +30,7 @@ To keep your metadata organized, we recommend the following folder structure ("T
   <File name="package.json" />
   <File name="tsconfig.json" />
   <File name="objectstack.config.ts" />
-</Files>
+</FileTree>
 
 ## Key Concepts