docs(api): fix electronics drift in ProductCategory enum

[LKSNDRTMLKV]

Summary

ProductCategory in the OpenAPI spec is a hand-maintained, cross-sector enum on PassportResponse.productCategory. Its electronics values had drifted: it carried laptop and charger but was missing tablet, monitor, tv, server, and earphone — incomplete even against what's actually pinned today.

• Added the five missing electronics values so the enum matches the currently-pinned dpp-domain catalog.
• Added a note that this whole field mirrors dpp-domain::Passport.product_category, which the core library has already removed upstream (zero production readers there) — every write path here already sets it to null, so the field is dead in practice regardless of its listed values, and it's slated for removal from this spec once the pinned core version picks up that change. Not removing it now since that's bundled with the core-pin bump, a separate piece of work.

Scoped to the electronics values only — the battery-related entries (ev_battery/industrial_battery/lmt_battery) weren't part of what was checked this pass and are left untouched.

Test plan

• just openapi-check (Redocly lint) green

[codacy-production]

Up to standards ✅

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[LKSNDRTMLKV]

Superseded by #108, which removes the ProductCategory schema and the productCategory property outright rather than annotating them.

This PR's own note said the field was slated for removal once the pinned core version picked up core's removal of Passport.product_category — #108 is that repin, so the annotation would describe a field the spec no longer has.