Adjust initial AI streaming status

[hanna-paasivirta]

Description

This PR changes the initial progress status shown to the user when starting a conversation with the AI assistants from "Generating response..." to "Thinking..." . This change is required because we are adding a more detailed stream of status updates from Apollo, where "Generating response" would feel out of place. OpenFn/apollo#452

Validation steps

1. Start a conversation with any AI assistant. Check that the first status that gets shown is "Thinking..."

AI Usage

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• I have used Claude Code
• I have used another model
• I have not used AI

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Pre-submission checklist

• I have performed an AI review of my code (we recommend using /review
  with Claude Code)
• I have implemented and tested all related authorization policies.
  (e.g., :owner, :admin, :editor, :viewer)
• I have updated the changelog.
• I have ticked a box in "AI usage" in this PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.59%. Comparing base (2f1a43e) to head (67d8d6d).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4630      +/-   ##
==========================================
- Coverage   89.61%   89.59%   -0.02%     
==========================================
  Files         444      444              
  Lines       21505    21505              
==========================================
- Hits        19272    19268       -4     
- Misses       2233     2237       +4     

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[josephjclark]

Should we cycle it, rather than using a static value?

How long does it take to get the first response back from apollo?

Should we say Calling assistant or something to imply "we're uploading your question"? Because it's not really thinking yet, it's just taking the input and preparing to think.

Maybe that doesn't matter much but "Thinking" is a) boring b) not very insightful. So I'm just wondering if there's something cheap we can use instead