chore: bump Go 1.24.4 → 1.26.3, Alpine 3.21 → 3.23

Go 1.24 EOL since Feb 2026. Fixes 33 stdlib vulns found by
govulncheck (database/sql, os/exec, net/http). Gets Green Tea GC.

Dockerfile

@@ -1,5 +1,5 @@
 # --- Stage 1: Builder ---
-FROM golang:1.24-alpine3.21 AS builder
+FROM golang:1.26-alpine3.23 AS builder
 RUN apk add --no-cache gcc musl-dev
 WORKDIR /app
 COPY go.mod go.sum ./
@@ -15,7 +15,7 @@ RUN --mount=type=cache,target=/go/pkg/mod \
     go build -trimpath -ldflags="-s -w -X main.version=${VERSION} -X main.commit=${COMMIT} -X main.date=${BUILD_DATE}" -o uptop ./cmd/uptop/main.go
 
 # --- Stage 2: Runner ---
-FROM alpine:3.21
+FROM alpine:3.23
 WORKDIR /app
 RUN apk add --no-cache ca-certificates openssh-client
 RUN mkdir /data