Restore imported trackers and add force recheck

[thedancingdeveloper]

Summary

• add tracker URLs to existing torrents at runtime, persist them across JSON/Postgres session reloads, and immediately start announcing live torrents
• add native and qBittorrent-compatible force-recheck endpoints while preserving paused/live state
• expose Force Recheck in the torrent right-click menu with disabled-state handling
• cover tracker validation, persistence, live announces, integrity checks, API handlers, and WebUI interactions

Root cause

qBittorrent stores effective tracker lists in .fastresume files when the exported .torrent metainfo has no announce fields. rustTorrent therefore imported valid payload/metainfo but had no tracker data to retain. The new tracker API provides a safe recovery path and persists recovered trackers.

Verification

• cargo fmt --all -- --check
• cargo clippy --workspace --exclude rtbit-desktop --no-default-features --features default-tls -- -D warnings
• cargo test --workspace --exclude rtbit-desktop --no-default-features --features default-tls
• WebUI build, unit tests, lint (existing warnings only), and 7 Playwright tests