add direct torrent intake, metadata cache, and explainable autopilot

[melqtx]

What changed

• Accept magnets, infohashes, local torrent files, and torrent URLs directly.
• Cache validated metainfo with bounded storage and strict filesystem checks.
• Make autopilot plans explainable, constrained, confirmed, and locally auditable.
• Improve metadata discovery status, early queueing, cache diagnostics, and HTTP size limits.