feat(swarm): add decnet swarm deckies to list deployed shards by host

`swarm list` only shows enrolled workers — there was no way to see which
deckies are running and where. Adds GET /swarm/deckies on the controller
(joins DeckyShard with SwarmHost for name/address/status) plus the CLI
wrapper with --host / --state filters and --json.

decnet/web/db/models.py

@@ -307,6 +307,20 @@ class SwarmHostView(BaseModel):
     notes: Optional[str] = None
 
 
+class DeckyShardView(BaseModel):
+    """One decky → host mapping, enriched with the host's identity for display."""
+    decky_name: str
+    host_uuid: str
+    host_name: str
+    host_address: str
+    host_status: str
+    services: list[str]
+    state: str
+    last_error: Optional[str] = None
+    compose_hash: Optional[str] = None
+    updated_at: datetime
+
+
 class SwarmDeployRequest(BaseModel):
     config: DecnetConfig
     dry_run: bool = False