deps: bump Go to 1.26.4 across go.mod, Dockerfiles, GH Actions

Workspace-wide sync. luxfi/node already shipped on 1.26.4 in v1.30.6
(commit 121aca1fa9); this is the cross-repo catch-up.

.github/workflows/ci.yml

@@ -49,7 +49,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        go-version: ['1.26.3']
+        go-version: ['1.26.4']
     steps:
       - name: Checkout code
         uses: actions/checkout@v4

Dockerfile

@@ -1,5 +1,5 @@
 # Build stage
-FROM golang:1.26.3-alpine AS builder
+FROM golang:1.26.4-alpine AS builder
 
 # Install build dependencies
 RUN apk add --no-cache git make