Fix schema_app forcing the creation of a schemas/ dir

[OCopping]

When running any part of the app, schema_app is imported into the top level typer app, which caused SCHEMAS_DIR.mkdir() to be called. This causes the jsonmap generation command to fail as the command is run in a read-only mounted directory.

[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.83%. Comparing base (7974e79) to head (7aa27b6).

Files with missing lines	Patch %	Lines
src/techui_builder/schema_generator.py	62.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #254      +/-   ##
==========================================
- Coverage   96.11%   95.83%   -0.28%     
==========================================
  Files          13       13              
  Lines         978      985       +7     
==========================================
+ Hits          940      944       +4     
- Misses         38       41       +3     

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