fix(web): clear changes views after deleting all sessions

[ravshansbox]

Issue for this PR

Closes #14860

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Problem: After deleting all sessions and navigating back to the session list (where params.id is undefined), the following views still display stale content instead of being empty:

• Session changes view
• Last turn changes view
• Changes view

Root Cause:

1. The SessionReview component's local store is initialized with initial diffs and doesn't clear itself when diffs become empty
2. The tree state (tracking activeDiff, pendingDiff, reviewScroll) is only cleared when sessionKey changes, but not when params.id becomes undefined

Changes:

1. SessionReview component (packages/ui/src/components/session-review.tsx):

   • Added effect to clear local store.open state when props.diffs becomes empty
   • This ensures the component's internal state resets when no diffs are available

2. Session page (packages/app/src/pages/session.tsx):

   • Added effect to clear tree state (reviewScroll, pendingDiff, activeDiff) when params.id is undefined
   • This ensures diff tracking state is cleared when navigating away from a session

How did you verify your code works?

Verified that after deleting all sessions and navigating back to the session list:

• All changes views are completely empty
• No stale content is displayed
• The review panel shows the empty state

Screenshots / recordings

N/A

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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