* fix(release): repair root-owned artwork and plugins folders on upgrade
Navidrome 0.57.0, 0.60.x and 0.61.x created the plugins and artwork folders as soon as the configuration loaded. The deb/rpm postinstall script runs navidrome as root, so fresh installs and upgrades on those versions left these folders owned by root. The service runs as the navidrome user and cannot write to them. Since 0.64.0 new artwork is stored under artwork/hashed, so affected installs fail to persist artwork and cannot read the plugins folder.
The postinstall script now changes the owner of these two folders to navidrome, only when they exist and are owned by root. The change is not recursive: root created the folders empty and the service could never write inside them, so fixing the folder itself is enough and stays instant regardless of how much artwork exists. Folders an admin assigned to another user are left untouched.
Fixes#6140
* fix(release): handle root-owned cache folder without install noise
The postinstall script ran an unconditional chown on /var/lib/navidrome/cache during fresh installs. Since folders are created lazily, the cache folder does not exist at that point, so every fresh deb/rpm install printed "chown: cannot access '/var/lib/navidrome/cache': No such file or directory".
The cache folder is now part of the same root-owned folder check used for artwork and plugins: it is fixed when it exists and is owned by root, and skipped silently otherwise. This also covers installs from 0.54.1 and 0.54.2, which created the cache folder as root before the chown was added.
* fix(release): never follow symlinks when repairing folder ownership
The ownership check used find's default -P mode, so -user root tested a symlink itself, while chown dereferenced it. A root-owned symlink pointing to a folder owned by another account made the postinstall script reassign that folder to navidrome, bypassing the root-owner guard.
The check now only matches real directories (-type d without following links) and uses chown -h. Following the link with find -H was rejected: /var/lib/navidrome is owned by navidrome, so the service account could plant a symlink to any root-owned directory and have the next upgrade hand it over. As a trade-off, a symlink to a root-owned folder is no longer repaired; the folders affected by the original bug were always real directories.
