Add comprehensive D4D datasheet for Bridge2AI-Voice dataset

- Created detailed datasheet for Bridge2AI-Voice v1.1
- Extracted metadata from PhysioNet and Health Data Nexus documentation
- Includes comprehensive coverage of all D4D sections:
  * Motivation and purpose
  * Dataset composition (12,523 recordings, 306 participants)
  * Collection process and protocols
  * Preprocessing and derived data details
  * Privacy protections and HIPAA Safe Harbor de-identification
  * Intended uses and limitations
  * Access requirements and licensing
  * Funding, citations, and references
- Follows structure of existing VOICE D4D files in repository

Co-Authored-By: Claude <noreply@anthropic.com>

Author: d4dassistant