Clean up dead Go code in handlers, pages, and stores

- Remove "chat" from surface disable guard (only admin needs it)
- Remove "chat" from IsSurfaceEnabled always-on check
- Remove unused fmt.Sprintf references in team stores
- Update stale comments referencing personas and chat surfaces

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

server/pages/pages_surfaces.go

@@ -48,11 +48,10 @@ func (e *Engine) SeedSurfaces() {
 }
 
 // IsSurfaceEnabled checks if a surface is enabled in the registry.
-// Chat and Admin are always enabled (system-critical).
+// Admin is always enabled (system-critical).
 // Returns true if the surface is not found (fail-open for backward compat).
 func (e *Engine) IsSurfaceEnabled(surfaceID string) bool {
-	// Chat and Admin cannot be disabled — they're system-critical
-	if surfaceID == "chat" || surfaceID == "admin" {
+	if surfaceID == "admin" {
 		return true
 	}
 	if e.stores.Packages == nil {