Initial public release.

• Renames recognized IMSLP PDF downloads with readable filenames.
• Includes a visual, drag-and-drop filename builder with composer, work title, catalogue number, instrument or part, edition, IMSLP ID, and custom text fields.
• Preserves classic-format behavior while supporting configurable custom formats.
• Adds conservative direct-download fallbacks, filename sanitization, duplicate handling, and length limits.
• Keeps all preferences and temporary metadata locally and transmits no data.