feat(web-ui): show decky IP on SwarmDeckies, drop compose-hash column

Operators want to know what address to poke when triaging a swarm decky;
the compose-hash column was debug scaffolding that never paid off.

DeckyShard has no IP column (the deploy-time IP lives on DecnetConfig),
so the list endpoint resolves it at read time by joining shards against
the stored deployment state by decky_name. Missing lookups render as "—"
rather than erroring — the list stays useful even after a master restart
that hasn't persisted a config yet.

decnet/web/db/models.py

@@ -333,6 +333,7 @@ class SwarmHostView(BaseModel):
 class DeckyShardView(BaseModel):
     """One decky → host mapping, enriched with the host's identity for display."""
     decky_name: str
+    decky_ip: Optional[str] = None  # resolved from the stored DecnetConfig at read time
     host_uuid: str
     host_name: str
     host_address: str