feat: forward decky.*.service.* on per-topology SSE stream

The /topologies/{id}/events SSE proxy now subscribes to two bus
patterns concurrently and merges them through a bounded asyncio.Queue:

* topology.{id}.>  — lifecycle (status, mutation.*) — unchanged.
* decky.>          — per-decky events, filtered by payload.topology_id
                     so a fleet decky sharing a name with a topology
                     decky doesn't leak across.

_sse_name_for routes 'decky.<name>.service.added' to the SSE event
name 'decky.service.added' (kept the prefix so the frontend doesn't
collide with topology lifecycle events that share leaf names like
'status').

useTopologyStream surfaces the two new event names; MazeNET.tsx's
onStreamEvent optimistically patches the matching node's services
list so a second tab reflects shape changes without a refetch.

decnet_web/src/components/MazeNET/useTopologyStream.ts

@@ -16,7 +16,13 @@ export type TopologyStreamEventName =
   | 'mutation.applying'
   | 'mutation.applied'
   | 'mutation.failed'
-  | 'status';
+  | 'status'
+  // Live per-decky service mutations forwarded by the SSE proxy on the
+  // server.  The payload carries decky_name + service_name + the
+  // post-mutation services list, so a second tab can reconcile shape
+  // without a refetch.
+  | 'decky.service.added'
+  | 'decky.service.removed';
 
 export interface TopologyStreamEvent {
   name: TopologyStreamEventName | string;
@@ -40,6 +46,8 @@ const NAMED_EVENTS: TopologyStreamEventName[] = [
   'mutation.applied',
   'mutation.failed',
   'status',
+  'decky.service.added',
+  'decky.service.removed',
 ];
 
 export function useTopologyStream({