Streamline show table

[ahuang11]

Makes finding the user message and removing the need to determine join a bit more robust.

Before:

After:

No longer startswith because the planner now mutates the user message with additional instructions.

3 (u). "Show the table: 'passengers.csv'" -- Here's the current instructions from the multi-step plan: "Generate and execute a query to retrieve all data from the 'passengers.csv' table."

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.

Project coverage is 51.59%. Comparing base (82df710) to head (f45e0dd).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
lumen/ai/agents.py	0.00%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #907      +/-   ##
==========================================
- Coverage   51.66%   51.59%   -0.07%     
==========================================
  Files         108      108              
  Lines       13701    13718      +17     
==========================================
  Hits         7078     7078              
- Misses       6623     6640      +17     

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