forked from unom/punktfunk
M1 of design/library-scanner-plugins-implementation-plan.md — behavior-frozen groundwork for lifting the six scanners out into plugins. WP1.1: heroic_command/heroic_launch_prefix, epic_launch_uri, gog_spawn, valid_steam_appid and shortcut_gameid move into library/launch.rs with their unit tests. The scanner modules beside it now do enumeration only, so they can be deleted wholesale later without taking launch logic with them (D1). WP1.2: is_local_art_path accepts file:// (the plugin contract) and POSIX absolute paths, excluding the two /-leading shapes the host itself emits (its own /api/ proxy path and protocol-relative CDN URLs). local_art_bytes percent-decodes and converts a file:// value first. The art proxy and fetch_box_art resolve ANY id against library.json before the legacy steam: branch, so a plugin's entries serve art without the host knowing its store. No API change; no user-visible change.