Add sql context

[ahuang11]

Closes #889

Motivated by if user changes the spec a lot, (or even a little, change max to min) the table name may not be relevant, so the LLM should be able to look at the SQL for the source of truth.

Fixes a bug where create_sql_expr_source doesn't set ephemeral=True.

Also, provides additional SQL context for ephemeral tables in Planner. The planner can additionally look at the non-eph tables' schemas if requested

Lastly, it uses consistent formatting across templates

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 51.66%. Comparing base (3b580de) to head (71e9391).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
lumen/ai/utils.py	0.00%	6 Missing ⚠️
lumen/ai/coordinator.py	0.00%	5 Missing ⚠️
lumen/ai/models.py	0.00%	1 Missing ⚠️
lumen/sources/duckdb.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #890   +/-   ##
=======================================
  Coverage   51.66%   51.66%           
=======================================
  Files         108      108           
  Lines       13697    13700    +3     
=======================================
+ Hits         7076     7078    +2     
- Misses       6621     6622    +1     

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