Category rows crossed the DB-worker IPC boundary with Drizzle's camelCase
property names while the renderer contracts declare snake_case, so backup
export dropped hidden-category IDs and restore degraded to a type-only
match that hid every category. Project category ops to the declared wire
shape, normalize restore state from untrusted sources (dropping entries
without a numeric xtreamId), reject entries with missing user-state
collections, and add full export→import round-trip coverage (unit
manifest-equality + Electron e2e) plus regression tests.
Closes#1017
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>