pat-filemanger use @plone/client for standard restapi calls

[petschki]

hybrid implementation

Volto's aurora @plone/client (2.0.0-alpha.4) dropped the React/react-query dependency, so it is usable in this Svelte/Patternslib bundle. Route the standard restapi calls through the official client; keep the calls the alpha client can't yet express on the native-fetch request() layer. All calls already funnel through src/api/*, so this is a contained refactor of that layer.

• api/ploneClient.js: shared client (initialize with apiPath=portalUrl, apiSuffix="" → no /++api++), client()/toPath()/unwrap(); unwrap returns the axios .data and maps the client's {status,data,location} rejection to a RestapiError so callers keep .message/.status/.body. App.svelte inits it before any store runs.
• Migrated: fetchBreadcrumbs→getBreadcrumbs, pasteItems→move/copyContent, deleteItem→deleteContent, moveItem→updateContent{ordering}, createFolder→ createContent. Methods are called on the instance (services read this.config).
• Kept custom (alpha client can't express yet): the sorted/batched listing, workflow transitions, rearrange/set-default-page, tags/properties/rename, link integrity, and tus upload. The two transports coexist by design.
• docs/upstream-plone-client.md: ready-to-submit diffs+descriptions for the four wrapper gaps so the rest can migrate once released.
• Tests mock ./ploneClient.js at the api boundary; a jest manual mock at src/mocks/@plone/client.js auto-stubs the package (its CJS build pulls in ESM-only query-string jest can't load). Suite green; dev build compiles. The pattern is dynamically imported, so axios/zod land in the lazy filemanager chunk — core bundle ~unchanged.