Add Netflix viewing-history CSV import

[ALeonard9]

Story

As a druthers user, I want to import my downloaded Netflix viewing-history CSV so that I can add previously watched titles without searching for each one manually.

Acceptance Criteria

• Accept a Netflix viewing-history CSV downloaded from the user's Netflix account and validate the expected columns before processing.
• Match movie and TV rows against the Druthers catalog, showing matched, already tracked, ambiguous, and unmatched rows separately.
• Preview only net-new matches before writing anything to the user's library.
• Let the user add selected net-new matches or add all, without duplicating existing tracked items.
• Report skipped and unmatched rows clearly enough for manual follow-up, and make re-importing the same CSV idempotent.

Context

Raw capture (2026-08-05):

"More add types. Single add (current). Multi-add, which would stay on the search page, allowing multiple adds, and import, which would take an extract from IMDb or Netflix etc, and show net new movies and allow multi-add or add all."

Adam clarified that the Netflix source is the downloaded Netflix CSV export.

Related to #140, which covers IMDb CSV import and should provide a reusable importer precedent. Related to ALeonard9/druthers-web#168, which covers multi-item selection on catalog search rather than file import.

Channel Impact

• Web: In this issue — upload, match preview, and add-selected/add-all are part of the reference workflow.
• iOS: No impact — imported titles appear through existing library APIs; native CSV upload is not required for the initial workflow.
• MCP: No impact — local file upload and interactive match resolution are not appropriate additions to the existing discrete catalog tools.

Estimate

• Recommended model: Opus 4.8 — full-stack importer with external-format parsing, cross-domain matching, and user-data integrity concerns
• Human effort: M — requires a real Netflix export for manual verification and one UX review of ambiguous-match handling

Notes for Implementation

Use a real Netflix viewing-history CSV during local verification. Preserve the source rows until the user confirms the preview; do not write matched items during parsing.