feat: thinking block designs should occupy lesser space

[uinstinct]

Description

Makes thinking blocks occupy less space using the same design as tool calls.

• makes thinking block same as simple tool call ui
• replaces reasoning with thinking block peek

resolves CON-4521

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Checklist

• [] I've read the contributing guide
• [] The relevant docs, if any, have been updated or created
• [] The relevant tests, if any, have been updated or created

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Summary by cubic

Make thinking blocks more compact by matching the simple tool call UI, reducing vertical space and improving readability. Addresses CON-4521.

• Refactors
  • Replace Reasoning with ThinkingBlockPeek in StepContainer; remove Reasoning.tsx.
  • Restyle ThinkingBlockPeek to match tool call UI; collapsed by default with a small toggle.
  • Keep behavior: animated thinking state, elapsed time, token count, and redacted messaging.
  • Avoid duplicate redacted blocks and cap expanded height.

^{Written for commit 302ffb88752055eccfec9a941c003a263d534e23. Summary will update automatically on new commits.}