feat(session-ui): expose reasoning and tool details behind collapsible block

[kostaris]

Issue for this PR

Closes #21549, #21548

Type of change

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

What does this PR do?

1. Wraps model reasoning parts in a collapsible BasicTool card titled "Thinking" with brain icon and live status.
2. Sets allowOpenWhilePending on reasoning cards so users can expand thinking output while the assistant streams.
3. Preserves user open/close toggle state across virtualized list scroll and remounts via props.toolOpen and props.onToolOpenChange.
4. Enables collapsible output viewing for webfetch, task, and skill tools while keeping direct task subsession navigation on the arrow action link.
5. Adds tests for reasoning visibility and default open state.

How did you verify your code works?

• Ran bun test packages/app/src/pages/session/timeline/reasoning-visibility.test.ts.
• Ran bun turbo run typecheck.
• Tested expanding reasoning while streaming and after scrolling.

Screenshots / recordings

N/A

Checklist

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

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found a potentially related PR:

PR #46344: feat(app): collapsible reasoning cards
#46344

This appears to be related to the current PR #46657 as it addresses the same feature area - making reasoning cards collapsible in the session UI. This may be an earlier iteration or alternative approach to the same feature.