Universal SdPath Addressing

Description

Implement SdPath, the universal addressing system for the VDFS. This enum provides a core abstraction that makes device boundaries transparent, supporting both direct physical paths (device_id + path) and abstract content-aware paths.

Implementation Notes

• The SdPath enum and its methods are fully defined in src/domain/addressing.rs.
• The system includes helper methods like .is_local(), .as_local_path(), and .display() for ergonomic use.
• URI parsing (SdPath::from_uri) will be implemented to handle sd:// schemes for both physical and content paths.

Acceptance Criteria

• SdPath enum can represent both physical and content-based addresses.
• The system can differentiate between local and remote physical paths.
• URI strings can be reliably parsed into SdPath objects.