chore: bump Go toolchain to 1.26.5 for govulncheck (#69)

Fixes GO-2026-5856 (crypto/tls ECH privacy leak) and
GO-2026-4970 (os symlink root escape), both resolved in the
Go 1.26.5 standard library.

Author: andrewkroh

go.mod

@@ -1,6 +1,6 @@
 module github.com/andrewkroh/fleetpkg-mcp
 
-go 1.26.4
+go 1.26.5
 
 require (
 	github.com/andrewkroh/go-ecs v0.0.0-20260204044457-2d67483e976a