Add missing SQLite migration Designer.cs file

The SyncDailyPlanAndUserActivity migration was never discovered by
EF Core on mobile because its .Designer.cs companion file was missing.
Without this file, MigrateAsync() skips the migration entirely, leaving
DailyPlanCompletion without the UserProfileId column.

Generated from the existing ApplicationDbContextModelSnapshot.cs.

Verified on iOS simulator: all 3 SQLite migrations now apply correctly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: davidortinau