Onboarding's "Fertig" button was failing with two distinct errors:
1. Feed fetch hit `http://mana-api:3060/api/v1/news/feed` (the SSR-only
internal Docker hostname) and was blocked by CSP. The news client was
reading `$env/dynamic/public.PUBLIC_MANA_API_URL`, which on the client
resolves to whatever the SSR process had — i.e. the internal hostname.
Switched to the existing `getManaApiUrl()` helper, which on the client
reads `window.__PUBLIC_MANA_API_URL__` (set from
`PUBLIC_MANA_API_URL_CLIENT` = `https://mana-api.mana.how`).
2. `completeOnboarding` passed Svelte 5 `$state` proxy arrays directly
into the preferences store, which then handed them to Dexie's update
hook → `_pendingChanges.add` → `DataCloneError`. The picked arrays
are now snapshotted with `$state.snapshot()` at the call site, and
the store-side setters defensively spread their inputs so any future
caller is safe by default.
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