v0.8.1: PdmError Structured Error Enum

What's Changed

PdmError Structured Error Enum

Replaced Result<T, String> with PdmResult<T> across the entire Rust backend, introducing a typed PdmError enum with 10 variants:

• Cancelled — download cancelled by user
• Http(u16) — HTTP status code error
• ClientBuild(String) — HTTP client construction failure
• Probe(String) — URL probe failed
• NotFound(u64) — download not found
• Db(String) — database error
• Config(String) — configuration error
• Io(String) — I/O error
• Network(String) — network error
• Other(String) — generic fallback

Automatic conversion via From impls for reqwest::Error, rusqlite::Error, io::Error, String, &str, PoisonError, and serde_json::Error. The Tauri command layer (cmd.rs) retains String for IPC compatibility.

Files Changed

• types.rs — PdmError enum, Display, Error trait, From impls, PdmResult alias
• db.rs — all methods return PdmResult
• download_manager.rs — all methods return PdmResult
• engine/mod.rs — DownloadEngine trait returns PdmResult
• engine/concurrent.rs — download() returns PdmResult, typed errors
• engine/single.rs — uses PdmError::Cancelled/Http/Io/Network
• worker.rs — add_with_id returns PdmResult
• probe.rs — returns PdmResult
• config.rs — save() returns PdmResult
• cmd.rs — DM calls use .map_err for Tauri IPC boundary

Full Changelog: v0.8.0...v0.8.1