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.

Dockerfile

@@ -9,7 +9,7 @@
 # resulting dist/ into this build context. ui/embed.go imports the
 # bundle via //go:embed all:dist at compile time.
 
-FROM golang:1.26-alpine AS go-build
+FROM golang:1.26.4-alpine AS go-build
 WORKDIR /src
 COPY go.mod go.sum ./
 RUN go mod download

go.mod

@@ -1,6 +1,6 @@
 module github.com/hanzoai/tasks
 
-go 1.26.3
+go 1.26.4
 
 retract (
 	v1.30.0