fix(bus): topic segments can't contain dots — service.added → service_added

Bus topic segments are NATS-style tokens and the validator at
bus/topics.py:402 rejects '.', '*', '>', whitespace.  My W3 constants
'service.added' / 'service.removed' tripped this on every live
add/remove call:

  ValueError: topic segment 'service.added' may not contain '.', ...

Renamed both to underscore form: DECKY_SERVICE_ADDED = 'service_added'.
Aligned the SSE forwarder's name mapping (decky.<name>.service_added →
SSE event 'decky.service_added') and the frontend's
useTopologyStream listener + MazeNET.tsx event handler.  Also updated
the wiki entry with a note about the underscore.

decnet_web/src/components/MazeNET/MazeNET.tsx

@@ -679,8 +679,8 @@ const MazeNET: React.FC = () => {
     // patch local state so the chip set reflects shape without a full
     // re-hydrate.  The post-mutation services list lives on the
     // payload; same shape the actor's POST/DELETE response carries.
-    if (event.name === 'decky.service.added'
-      || event.name === 'decky.service.removed') {
+    if (event.name === 'decky.service_added'
+      || event.name === 'decky.service_removed') {
       const p = event.payload ?? {};
       const deckyName = typeof p.decky_name === 'string' ? p.decky_name : null;
       const services = Array.isArray(p.services) ? p.services as string[] : null;

decnet_web/src/components/MazeNET/useTopologyStream.ts

@@ -21,8 +21,8 @@ export type TopologyStreamEventName =
   // 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';
+  | 'decky.service_added'
+  | 'decky.service_removed';
 
 export interface TopologyStreamEvent {
   name: TopologyStreamEventName | string;
@@ -46,8 +46,8 @@ const NAMED_EVENTS: TopologyStreamEventName[] = [
   'mutation.applied',
   'mutation.failed',
   'status',
-  'decky.service.added',
-  'decky.service.removed',
+  'decky.service_added',
+  'decky.service_removed',
 ];
 
 export function useTopologyStream({