Discord (Shdjfgatdif, standalone): some downloads complete on disk but get marked failed with
"File not found on disk after 5 search attempts. Expected: <basename>" — which tells the user
nothing about where we looked or what to check.
This is deliberately a DIAGNOSTIC fix, not a behavior change. The finder + path handling are sound
(verified: docker_resolve_path no-ops in standalone, the finder walks the configured
soulseek.download_path and resolves a present file). When it still misses after slskd reported the
transfer Succeeded, the cause is environmental — either the file is still landing (timing) or, the
classic standalone gotcha, SoulSync's download_path doesn't point at slskd's actual download dir.
Neither is something our code can "fix"; the user fixes the config, or the file arrives.
So: name the folder we actually searched and spell out the two real causes, turning an opaque
failure into self-diagnosis ("oh, my download folder's wrong"). Retry/wait behavior is left
untouched on purpose — widening the window does nothing for a path mismatch and I can't justify it
for this user. Also normalizes the slskd backslash path so the reported filename is the leaf, not
the whole "@@@user\folder\file" string.
Updated the existing not-found test to pin the new actionable message (searched path + config
hint + filename). 588 downloads tests green, ruff clean.
b07359cdb5