fix(storage): detect overview language from child summaries

[qin-ctx]

Description

Fix directory overview language detection for resource directories that contain only child directories. The semantic processor now considers child directory abstracts when resolving the output language, so Chinese-only directory trees do not fall back to English just because there are no direct file summaries.

Related Issue

N/A

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Include child directory abstracts in overview output-language detection.
• Keep file summaries as the primary detection source when present.
• Fall back to the directory name only when neither files nor child summaries exist.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Command run:

.venv/bin/python -m pytest tests/storage/test_semantic_processor_language.py

Result: 33 passed, 4 existing warnings.

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

N/A

Additional Notes

This PR intentionally keeps the fix scoped to semantic_processor.py only.

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