Resync the vendored backend types

[ClaydeCode]

What

Regenerates shard_core/data_model/backend from freeshard-controller main (0ec6c6a).

Why now

The drift-check job compares this directory against controller main byte for byte, and
it is currently red on every PR opened against main — #173 and #240 both fail it.
#180 and #181 show green only because their runs predate the drift. So this is not one
branch's problem; it blocks anything opened today.

What changed

Entirely the controller's shard-migration work, which is already deployed on the
controller side and simply was never regenerated here:

Change	File
Permission.MIGRATE_SHARD	permission_model.py
ShardStatus.CUTTING_OVER	shard_model.py
cloud on ShardUpdateDb	shard_model.py
new ShardMigration* models, statuses and exceptions	shard_migration_model.py (new)

Verification

• Generated by just get-types, not hand-edited.
• Purely additive: three insertions plus one new file, nothing removed or renamed.
• ruff check clean; the new module imports cleanly and both new enum members resolve.
• Nothing in shard_core imports shard_migration_model, and no code matches
  Permission or ShardStatus exhaustively, so the added members change no behaviour.
  The only consumer of ShardStatus outside the vendored dir is tests/conftest.py,
  which pins ASSIGNED.

Full suite not run locally for this one — it is generated vendored types with no importers;
CI covers it.

🤖 Generated with Claude Code