feat(db): add DeckyLifecycle table for async deploy/mutate tracking

One row per (decky, operation) attempt. State machine:
pending -> running -> succeeded | failed (+ error text). Rows are
append-only after terminal; retries write a new row.

Sibling of DeckyShard rather than a rework -- DeckyShard tracks
runtime container state observed via heartbeat, this tracks
operation lifecycle. New table, UUID PK.

Adds BaseRepository abstract methods (create_lifecycle,
update_lifecycle, get_lifecycle_by_ids, find_open_lifecycle,
sweep_stale_lifecycle) with SQLModelRepository mixin impl.
Backbone for the upcoming 202-Accepted async API.

decnet/web/db/models/__init__.py

@@ -82,6 +82,15 @@ from .decky import (
     ServiceConfigFieldDTO,
     ServiceSchemaResponse,
 )
+from .decky_lifecycle import (
+    DeckyLifecycle,
+    DeckyLifecycleListResponse,
+    DeckyLifecycleView,
+    LifecycleAcceptedResponse,
+    LifecycleDelta,
+    LifecycleOperation,
+    LifecycleStatus,
+)
 from .fleet import (
     LOCAL_HOST_SENTINEL,
     FleetDecky,
@@ -278,6 +287,14 @@ __all__ = [
     "FleetDecky",
     "ServiceConfigFieldDTO",
     "ServiceSchemaResponse",
+    # decky_lifecycle
+    "DeckyLifecycle",
+    "DeckyLifecycleListResponse",
+    "DeckyLifecycleView",
+    "LifecycleAcceptedResponse",
+    "LifecycleDelta",
+    "LifecycleOperation",
+    "LifecycleStatus",
     # health
     "ComponentHealth",
     "HealthResponse",