Multi-source Phase C2: onboarding wizard — populate-vs-empty + deep-history choice

[jozef2svrcek]

Phase C2 of multi-source (#40) — redesign the setup wizard's source step per the locked design (mockup discussed in #40).

Goal

Keep onboarding a simple binary, defer all detail to Maintenance → Sources (C1):

• Populate the reference database (recommended) vs Start with an empty database.
• "Populate" → one bundled acknowledgment screen listing the selected sources with per-source license/credit checkboxes (Lumbra's-style NC flagged where relevant), then the daemon imports in the background — onboarding finishes immediately (replaces today's inline "download TWIC with a progress bar" step).

Choices on the populate path

• Currency: TWIC + Lichess Broadcasts (auto).
• Deep history: Free (Caissabase once hosted — see Server-side source-manifest service (Lumbra's, Bundesliga) — decouple fragile URL discovery from app releases #94; Ajedrez OTB as the shipped interim/alternative) · I own a commercial DB (e.g. ChessBase Megabase → export to PGN → import via the existing local-import path; optionally set its cutoff so the partition caps the live feeds) · None.
• (Correspondence: same Free/own/None pattern — later, once its source exists.)

Notes

• Acknowledgment reuses the C1 credit_acked gate (sources_set_enabled with credit_acked).
• Commercial route needs no new backend — it's the existing import_pgn/local import, just surfaced in the wizard.
• Caissabase-as-default depends on its hosted PGN existing (Server-side source-manifest service (Lumbra's, Bundesliga) — decouple fragile URL discovery from app releases #94); until then "Free" = Ajedrez.
• Touch-points: SetupWizard.tsx (the TWIC step → a sources step), reuse SourcesPanel/api helpers where sensible.