Move CLI defaults to cli.py and refactor ls.py parameter handling

[asmacdo]

Context

Follow-up to #372 (duct_main.py breakup). Two constants remain in duct_main.py that are really CLI defaults:

• DUCT_OUTPUT_PREFIX - default for --output-prefix
• EXECUTION_SUMMARY_FORMAT - default for --summary-format

These should live in cli.py with the argument definitions, not in a separate module.

Proposed Changes

1. Rename constants to clarify they're defaults:

   • DUCT_OUTPUT_PREFIX → DEFAULT_OUTPUT_PREFIX
   • EXECUTION_SUMMARY_FORMAT → DEFAULT_SUMMARY_FORMAT

2. Move to cli.py - CLI defaults belong with CLI code

3. Refactor ls.py - Currently imports DUCT_OUTPUT_PREFIX to construct a glob pattern when no paths are given:

   pattern = f"{DUCT_OUTPUT_PREFIX[:DUCT_OUTPUT_PREFIX.index('{')]}*"

   This creates a circular import if the constant moves to cli.py (cli imports ls).

   Solution: Add a --search-prefix (or similar) CLI argument to con-duct ls and pass it as a parameter to the ls() function.

4. Update tests to import from the new location

Blocked By

• Refactor: Break up duct_main.py into smaller modules #385 should merge first