Prompt user to click Rerun if empty

[ahuang11]

Improves the UX slightly by offering the user a path forward by injecting an SQL comment mentioning the query is invalid so the Planner and SQLAgent knows on the second try.

Addresses #1197

🗃️ Current SQL:
```sql
SELECT * FROM "windturbines.parquet" ORDER BY "p_cap" DESC LIMIT 5
-- No data was returned from the query.

📋 Last table: top_5_pcap

[codecov]

Codecov Report

Attention: Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 55.79%. Comparing base (47a6a47) to head (eff2edf).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
lumen/ai/agents.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1215      +/-   ##
==========================================
- Coverage   55.80%   55.79%   -0.02%     
==========================================
  Files         113      113              
  Lines       17089    17094       +5     
==========================================
+ Hits         9537     9538       +1     
- Misses       7552     7556       +4     

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