Fix migration 28 crash when client_state.data column is absent

[Copilot]

Migration 28 unconditionally executes SELECT data FROM client_state WHERE id = 1 when upgrading an existing table, but users who ran an older version of migration 21 without the data column would hit OperationalError: no such column: data.

Changes

• migration_28.py: Before reading data, introspect the table schema via PRAGMA table_info(client_state). If the column is absent, skip data extraction and proceed directly to drop/recreate with the new multi-user schema.
• tests/test_sqlite_migrator.py: Added two tests:
  • test_migration_28_with_existing_data_column — verifies JSON data is correctly migrated to per-user key-value rows under system
  • test_migration_28_without_data_column — verifies migration completes without error and produces a clean new schema when data is absent

QA Instructions

Run the new tests directly:

pytest tests/test_sqlite_migrator.py::test_migration_28_with_existing_data_column tests/test_sqlite_migrator.py::test_migration_28_without_data_column -v

To reproduce the original failure: create a client_state table with only id and updated_at columns (no data), then run Migration28Callback — before this fix it raises OperationalError: no such column: data.

Merge Plan

This touches the DB migration chain. No schema version bump is needed — the fix is purely defensive logic within migration 28. Safe to merge independently.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

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[lstein]

works as advertised