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",

decnet/web/db/models/decky_lifecycle.py

@@ -0,0 +1,87 @@
+"""DeckyLifecycle table + DTOs.
+
+Tracks one row per (decky, operation) attempt — `deploy` or `mutate` —
+so the API can return 202 Accepted immediately and the wizard can poll
+state instead of holding an open HTTP request open for minutes.
+
+State machine: ``pending`` (row created, runner not yet started) →
+``running`` (runner picked it up) → terminal ``succeeded`` | ``failed``
+(+ ``error`` text).  Rows are immutable after terminal status; a retry
+writes a new row.
+
+Sibling of DeckyShard rather than a rework — DeckyShard tracks runtime
+container state observed via heartbeat, this tracks operation lifecycle.
+Per ``feedback_uuid_over_natural_keys``: new use case, new table, UUID PK.
+"""
+from __future__ import annotations
+
+import uuid
+from datetime import datetime, timezone
+from typing import Literal, Optional
+
+from pydantic import BaseModel, Field as PydanticField
+from sqlalchemy import Column, Text
+from sqlmodel import Field, SQLModel
+
+LifecycleOperation = Literal["deploy", "mutate"]
+LifecycleStatus = Literal["pending", "running", "succeeded", "failed"]
+
+
+def _now_utc() -> datetime:
+    return datetime.now(timezone.utc)
+
+
+class DeckyLifecycle(SQLModel, table=True):
+    """One row per (decky, operation) attempt."""
+
+    __tablename__ = "decky_lifecycle"
+
+    id: str = Field(
+        primary_key=True,
+        default_factory=lambda: str(uuid.uuid4()),
+    )
+    decky_name: str = Field(index=True)
+    # None for unihost / master-resident deckies.
+    host_uuid: Optional[str] = Field(default=None, index=True)
+    operation: str = Field(index=True)  # LifecycleOperation
+    status: str = Field(default="pending", index=True)  # LifecycleStatus
+    error: Optional[str] = Field(
+        default=None, sa_column=Column("error", Text, nullable=True),
+    )
+    started_at: datetime = Field(default_factory=_now_utc)
+    updated_at: datetime = Field(default_factory=_now_utc)
+    completed_at: Optional[datetime] = Field(default=None)
+
+
+# --- HTTP DTOs ---
+
+class DeckyLifecycleView(BaseModel):
+    """One lifecycle row, serialised for the wizard polling loop."""
+    id: str
+    decky_name: str
+    host_uuid: Optional[str] = None
+    operation: str
+    status: str
+    error: Optional[str] = None
+    started_at: datetime
+    updated_at: datetime
+    completed_at: Optional[datetime] = None
+
+
+class DeckyLifecycleListResponse(BaseModel):
+    rows: list[DeckyLifecycleView] = PydanticField(default_factory=list)
+
+
+class LifecycleAcceptedResponse(BaseModel):
+    """Returned by 202 deploy/mutate endpoints — lets the client subscribe
+    to the matching DeckyLifecycle rows via the polling endpoint."""
+    lifecycle_ids: list[str]
+
+
+class LifecycleDelta(BaseModel):
+    """One per-decky completion record in a worker → master heartbeat."""
+    decky_name: str
+    operation: str
+    status: str  # one of LifecycleStatus, typically "succeeded" | "failed"
+    error: Optional[str] = None
+    completed_at: Optional[datetime] = None