fix: store history in an app-namespaced SwiftData store

[iuhoay]

Problem

Translation history could silently disappear. HistoryStore created its SwiftData database with a bare ModelContainer(for: HistoryItem.self) and no URL. For a non-sandboxed app that resolves to the shared ~/Library/Application Support/default.store — a path every other non-sandboxed app using a bare ModelContainer also writes to. When another app opens that file with its own schema, Core Data recreates the store and drops our HistoryItem table, wiping the user's whole history. (Observed in the wild: the shared file ended up holding another app's APIRequestModel entity, with no HistoryItem table left anywhere on disk.)

Fix

• Pin the store to Application Support/<bundle-id>/Lumo.store. A bundle-id-scoped path can't collide with another app, and also keeps the Debug "Lumo Dev" history separate from Release.
• On first launch with the new path, importLegacyHistory(from:into:) does a one-time, non-destructive rescue of any history still in the old shared store:
  • A read-only Core Data metadata probe first confirms the file actually holds our HistoryItem entity. If it holds another app's schema, nothing is touched.
  • The legacy store is opened allowsSave: false and never deleted.
  • Every step is best-effort — a failure just means an empty list, never a crash.

Tests

New LegacyStoreRescueTests suite (3 tests):

• imports rows from a matching legacy store (and leaves the file in place)
• skips a foreign-schema store — the safety property
• no-ops cleanly when the legacy file is missing

Full suite: Test run with 100 tests in 15 suites passed.

Note

History already lost before this fix is unrecoverable (the shared store was overwritten). The rescue only helps installs where the old history still survives. API-key storage is unchanged.

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