The Go base has to be 1.26 for what compiles the controller's code

builder and route-proxy both build from the mesh-controller repository's context,
so its go.mod is theirs, and `nats.go v1.54.0` puts that at `go >= 1.26`. Pinned at
1.25.14 they cannot compile it: the build machine's own build failed with "go.mod
requires go >= 1.26.0 (running go 1.25.14)".

Each moves to the 1.26.8 digest of the flavour it already used — alpine for
builder, debian for route-proxy — so nothing changes but the compiler version.

modules/builder/module.json

@@ -77,7 +77,7 @@
     "on": [
       {
         "arg": "GO_BASE",
-        "image": "golang@sha256:1ae0735f00daffa3aaf1363a5184c0d2dc55c78e3db4ec70241cdac97bf84b59"
+        "image": "golang@sha256:8ac98ca534ac3f51e1f420a1dd2c15e74c75cfa0f23f3ad27eb5d7236c349a0c"
       },
       {
         "arg": "ALPINE_BASE",

modules/route-proxy/module.json

@@ -173,7 +173,7 @@
     "on": [
       {
         "arg": "GO_BASE",
-        "image": "golang@sha256:699337d620559a59b4a2bb298ad59611e535d2ee755a34cf2d2a98f37578dc80"
+        "image": "golang@sha256:6c2a5538f964f1c82f97ad14988bf05de100d922d159d0e398b54c7b0ca0c6c9"
       },
       {
         "arg": "ALPINE_BASE",