The repo metadata 'platform' field was a hardcoded enum; changing the
taxonomy meant a code change + redeploy. Make it admin-configurable:
- modules/setting/metadata.go: new [metadata] PLATFORM_OPTIONS setting
(default joomla,dolibarr,go,npm,generic), loaded in loadCommonSettingsFrom
- routers/web/admin/metadata.go + templates/admin/metadata.tmpl: new
Admin -> Metadata page to edit the list (persisted to app.ini), with a
nav entry and route
- routers/web/repo/setting/metadata.go + template: platform dropdown now
reads from the setting; a repo's current value stays selectable even if
removed from the list (no silent drop)
Closes#777
jmiller