Fix #159: Resolve AttributeError in design_system and search blindnes…

[YangKuoshih]

Closes #159

Description of Changes

This PR addresses the two specific bugs reported in issue #159 that were causing the design system generator to crash and search queries to fail for short acronyms.

1. AttributeError Fix (design_system.py)

The Problem: When calling persist_design_system without an explicit project_name (defaulting to None), the execution attempted to run project_name.lower(), resulting in an AttributeError.
The Fix: Added explicit handling to fallback checking if project_name is not None else "default", ensuring a valid string is always present before string manipulation occurs.

2. Search Blindness Fix (core.py)

The Problem: The BM25 algorithm's tokenize function was dropping any search query terms with a length of 2 or less. This created "search blindness" for critical industry acronyms like UI, UX, 3D, and AI.
The Fix: Updated the length filter constraint in core.py from > 2 to > 1 to allow 2-letter tokens to be properly indexed and searched against the CSV database.

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QA & Testing Instructions

To verify these fixes locally, the following tests were conducted:

1. Testing project_name=None Fallback:
Ran a generation pass strictly passing no project name:
generate_design_system('SaaS dashboard', project_name=None, persist=True)

• Result: Successfully created the ./design-system/default/ directory and wrote MASTER.md without crashing.

2. Testing Search Blindness Fix:
Ran design system generations using 2-letter queries that were previously ignored:
generate_design_system('UI dashboard', persist=True)
generate_design_system('UX dashboard', persist=True)

• Result: The BM25 algorithm successfully parsed the queries, located the correct patterns in the CSV files, and generated tailored design systems for both "UI" and "UX" concepts without skipping the 2-letter terms.