fix(web): prevent active stage selection from being overridden on pol…

[kunaldevsahu]

What this PR does

This PR fixes an issue in the Deployment Details page where the selected stage was reset during live polling.

The implementation introduces intelligent default stage tracking using a React useRef to distinguish between users who are following the default active stage and users who have manually selected a different stage. This preserves manual stage selections while still allowing the UI to automatically advance when the user is following the deployment's default progression.

Why we need it

The deployment details page polls for updates every 4 seconds while a deployment is running. Each polling update refreshes the deployment object, causing the initialization effect to run repeatedly and reset the selected stage to the default active stage.

As a result, users are unable to inspect logs or details of another stage because their selection is overwritten on every polling cycle.

With this change:

• Users who manually select a stage keep their selection across polling updates.
• Users who are following the default active stage continue to automatically advance as the deployment progresses.
• Navigating to a different deployment still initializes the appropriate default active stage.

Which issue(s) this PR fixes

Fixes #7119

Does this PR introduce a user-facing change?

Yes

How are users affected by this change?

Users can inspect logs and details for any stage on the Deployment Details page without their selection being reset during live polling.

Is this a breaking change?

No.

How to migrate (if breaking change)

N/A.

[github-actions]

👋 Hi @kunaldevsahu, welcome to PipeCD and thanks for opening your first pull request!

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