dpkg-deb -c on the bundled .deb shows mycelium at /usr/bin/mycelium
(no triple suffix), next to the app launcher. Our previous resolver
only looked for the suffixed dev name in resource_dir, so the
installed app could not find its sidecar.
Probe order is now: directory of current_exe, then resource_dir,
then CARGO_MANIFEST_DIR/binaries, then $PATH, with both the plain
"mycelium" name and the dev-style "mycelium-<triple>" alias
checked at each location.
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