PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

The Signals overview guide explains the core APIs and reactive concepts, but it provides limited guidance on how to reason about Signals when designing applications.

In particular, the guide does not clearly explain:

• The mental model behind Signals as a reactive state graph.
• When to use computed versus effect.
• Why derived state should generally be modeled with computed.
• The conceptual distinction between Signals and RxJS.

Issue Number: N/A

What is the new behavior?

This PR adds conceptual guidance to the Signals overview guide, including:

A new "Mental model" section.
Guidance on preferring derivation over synchronization.
Recommendations for choosing between computed and effect.
A conceptual comparison between Signals and RxJS focused on use cases rather than APIs.

The goal is to help developers adopt the Signals programming model more effectively and avoid common architectural misunderstandings.

Does this PR introduce a breaking change?

• Yes
• No

Other information

This is a documentation-only change.