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/auth.go

@@ -490,7 +490,7 @@ func BootstrapAdmin(cfg *config.Config, s store.Stores, uekCache ...*crypto.UEKC
 		})
 		// If the actual password changed, the vault seal is stale. Probe it
 		// with the current password and destroy only if unwrap fails.
-		// Ensure handle exists (backfill for pre-v0.24.0 users)
+		// Ensure handle exists (backfill for users)
 		if existing.Handle == "" {
 			handle := auth.UniqueHandle(ctx, s.Users, models.HandleFromName(cfg.AdminUsername))
 			s.Users.Update(ctx, existing.ID, map[string]interface{}{"handle": handle})