docs: add client-side navigation pattern for use_server_future

[xsoheilalizadeh]

Summary

Adds documentation for using ReadSignal props with use_server_future when navigating between instances of the same component.

Problem

When navigating between same-component instances (e.g., Product A → Product B), use_server_future with plain props doesn't update content because the closure doesn't detect the prop change.

Solution

Shows the pattern of using ReadSignal props instead of plain props to enable reactivity.

Changes

• Added new "Client-Side Navigation" section after the streaming section
• Includes comparison of non-working vs working code
• Concise explanation of why signals are needed

This addresses a common issue developers face when building fullstack apps with Dioxus router.