LFS tokens bind to a key id that SQLite can reuse #303

internal/lfs binds a transfer token to ssh_keys.id and internal/httpd/lfs.go checks only that id. ssh_keys is INTEGER PRIMARY KEY without AUTOINCREMENT and keys are hard-deleted, so removing the newest key and adding another gives the new key the same id, and a stolen token works again for the rest of its hour (or carries another user's access if their key takes the id). Bind the token to the key's fingerprint as well and compare it on each request.