chore: strip remaining pre-fork version references

Second pass — removes chat-switchboard version numbers from config
field docs, section headers, file headers, and test comments. These
were pre-fork version tags that don't apply to switchboard-core.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/handlers/presence.go

@@ -1,6 +1,6 @@
 package handlers
 
-// presence.go — Heartbeat upsert and status query (v0.23.1)
+// presence.go — Heartbeat upsert and status query
 //
 // Clients POST /api/v1/presence/heartbeat every 30s while active.
 // GET  /api/v1/presence?users=id1,id2 returns current status.