docs: update banner frontmatter property documentation

Replace beta banner documentation with comprehensive banner property docs:
- Simple usage: banner: true or banner: "message"
- Advanced usage with intents (info, warning, success, error, note, launch, tip, check)
- Custom color overrides with examples
- Plant-themed examples per documentation guidelines
- Mark beta property as deprecated with migration guidance

Co-Authored-By: Deep Singhvi <[email protected]>

Author: devin-ai-integration[bot]

fern/products/docs/pages/customization/frontmatter.mdx

@@ -213,29 +213,84 @@ hide-feedback: true
   <img src="./on-page-feedback.png" alt="Leave feedback feature" />
 </Frame>
 
-## Beta banner
-<ParamField path="beta" type="boolean | string" required={false} default={false}>
-  Displays a yellow warning banner at the top of the page to indicate that the content is in beta or still being worked on. Set to `true` for a default message, or provide a custom message string.
+## Banner
+<ParamField path="banner" type="boolean | string | object" required={false}>
+  Displays a banner at the top of the page content. Can be set to `true` for a default warning banner, a string for a warning banner with custom message, or an object for full customization with different intents and colors.
 </ParamField>
 
-<CodeBlock title="Example beta banner with default message">
+### Simple usage
+
+<CodeBlock title="Default warning banner">
+```mdx
+---
+title: New Plant Species Guide
+banner: true
+---
+```
+</CodeBlock>
+
+<CodeBlock title="Custom message">
+```mdx
+---
+title: Experimental Plant Care API
+banner: This plant care API is experimental and may change without notice.
+---
+```
+</CodeBlock>
+
+### Advanced usage with intents
+
+<CodeBlock title="Info banner">
+```mdx
+---
+title: Plant Database Migration
+banner:
+  message: We're migrating to a new plant database. Some features may be temporarily unavailable.
+  intent: info
+---
+```
+</CodeBlock>
+
+<CodeBlock title="Success banner">
 ```mdx
 ---
-title: New Feature Documentation
-beta: true
+title: New Plant Identification Feature
+banner:
+  message: Our new AI-powered plant identification feature is now available!
+  intent: success
 ---
 ```
 </CodeBlock>
 
-<CodeBlock title="Example beta banner with custom message">
+Available intents: `info`, `warning`, `success`, `error`, `note`, `launch`, `tip`, `check`
+
+### Custom colors
+
+<CodeBlock title="Banner with custom colors">
 ```mdx
 ---
-title: Experimental API
-beta: This API is experimental and may change without notice.
+title: Seasonal Plant Guide
+banner:
+  message: Spring planting season has begun! Check out our seasonal recommendations.
+  intent: tip
+  color:
+    background: "#e8f5e9"
+    text: "#1b5e20"
+    border: "#4caf50"
 ---
 ```
 </CodeBlock>
 
+<Warning>
+Custom colors may not adapt well to dark mode. Use with caution and test in both light and dark themes.
+</Warning>
+
+### Deprecated: beta property
+
+<ParamField path="beta" type="boolean | string" required={false} default={false}>
+  **Deprecated.** Use `banner` instead. Displays a yellow warning banner at the top of the page to indicate that the content is in beta or still being worked on.
+</ParamField>
+
 ## Page logo
 <ParamField path="logo" type="object" required={false}>
   Override the site-wide logo for a page. Specify different logos for light and dark modes using absolute URLs.