Add qBittorrent end-to-end test harness for persistence refactor baseline

[josecelano]

Summary

Add a high-level end-to-end test that validates tracker behavior through a complete torrent-sharing scenario using real containerized BitTorrent clients (qBittorrent), with SQLite as backend.

This is subissue 1525-02 from the persistence overhaul EPIC.

Why

The persistence refactor changes storage behavior underneath the tracker. A real-client full download cycle (seeder uploads -> leecher downloads -> tracker records completion) provides regression coverage beyond protocol-level tests.

Scope

• Add compose scenario for tracker + qbittorrent-seeder + qbittorrent-leecher
• Add Rust runner binary to orchestrate full scenario
• Add shared docker compose wrapper for runner tooling
• Verify leecher obtains byte-identical payload
• Ensure unconditional teardown (docker compose down --volumes) on success/failure/panic
• Use unique compose project names and dynamic port discovery for parallel-safe execution
• Document local/CI execution workflow

Main Acceptance Criteria

• Runner completes a full seeder -> leecher transfer against containerized tracker
• Payload integrity is verified after download
• No orphaned containers/volumes on success or failure
• No fixed host ports; discovered dynamically
• Temporary files are isolated and deleted on exit
• cargo test --workspace --all-targets passes (or E2E explicitly excluded with documented opt-in)
• linter all exits 0

Spec

• docs/issues/1525-02-qbittorrent-e2e.md
• EPIC: Overhaul persistence #1525

Notes

Reference implementation exists in josecelano/torrust-tracker branch pr-1684-review (read-only behavioral reference).