Validates the priv/mob_plugin.exs manifest of the plugin project in the
current directory — a plugin author's pre-publish check.
mix mob.validate_pluginChecks (see MOB_PLUGINS.md): required top-level fields, every declared file
path exists, and the installed :mob satisfies the manifest's mob_version.
Advisory warnings cover single-platform components and declared
permissions/plist keys. Exits non-zero if any error is found — never silent.
A project with no priv/mob_plugin.exs is a tier-0 plugin (nothing to
validate) and the task says so.