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/models/ext_connection.go

@@ -1,6 +1,6 @@
 package models
 
-// ── Extension Connections (v0.38.1) ──────────────────
+// ── Extension Connections ──────────────────
 
 // ExtConnection represents a scoped credential/endpoint configuration
 // for extensions that integrate with external services. Same scope