[P3] AniList OAuth linking and import

[hazeliscoding]

Problem

Users who already track anime on AniList have no way to import their existing data. This is the single biggest value-add post-MVP.

Requirements

• AniList OAuth 2.0 flow to link accounts
• Import user's AniList watchlist into a watch space
• Map AniList statuses to BloomWatch statuses
• Handle duplicate detection (anime already added to the space)

Acceptance Criteria

• Users can link their AniList account from settings
• Watchlist import creates entries in the current watch space
• Duplicates are skipped or merged
• Import progress is shown to the user

References

• Roadmap §10 — Growth Features
• Architecture §5.5 — AniListSync module