fix(frontend): Rename "Tasks" tab to "Agents" in navbar (#11982)

## Summary
Renames the "Tasks" tab in the navbar to "Agents" per the Figma design.

## Changes
- `Navbar.tsx`: Changed label from "Tasks" to "Agents"

<img width="1069" height="153" alt="image"
src="https://github.com/user-attachments/assets/3869d2a2-9bd9-4346-b650-15dabbdb46c4"
/>


## Why
- "Tasks" was incorrectly named and confusing for users trying to find
their agent builds
- Matches the Figma design

## Linear Ticket
Fixes [SECRT-1894](https://linear.app/autogpt/issue/SECRT-1894)

## Related
- [SECRT-1865](https://linear.app/autogpt/issue/SECRT-1865) - Find and
Manage Existing/Unpublished or Recent Agent Builds Is Unintuitive

autogpt_platform/frontend/src/components/layout/Navbar/Navbar.tsx

@@ -47,7 +47,7 @@ export function Navbar() {
 
   const actualLoggedInLinks = [
     { name: "Home", href: homeHref },
-    ...(isChatEnabled === true ? [{ name: "Tasks", href: "/library" }] : []),
+    ...(isChatEnabled === true ? [{ name: "Agents", href: "/library" }] : []),
     ...loggedInLinks,
   ];