fix: upgrade Go to 1.25 for Caddy 2.10.2 compatibility

Caddy 2.10.2 requires Go 1.25 (declared in its go.mod). The previous
commit incorrectly downgraded to Go 1.23 based on the false assumption
that Go 1.25.5 doesn't exist.

This fix:
- Updates Dockerfile Go images from 1.23-alpine to 1.25-alpine
- Updates backend/go.mod to go 1.25
- Updates go.work to go 1.25

Fixes CI Docker build failures in xcaddy stage.

Dockerfile

@@ -48,7 +48,7 @@ RUN --mount=type=cache,target=/app/frontend/node_modules/.cache \
     npm run build
 
 # ---- Backend Builder ----
-FROM --platform=$BUILDPLATFORM golang:1.23-alpine AS backend-builder
+FROM --platform=$BUILDPLATFORM golang:1.25-alpine AS backend-builder
 # Copy xx helpers for cross-compilation
 COPY --from=xx / /
 
@@ -98,7 +98,7 @@ RUN --mount=type=cache,target=/root/.cache/go-build \
 # ---- Caddy Builder ----
 # Build Caddy from source to ensure we use the latest Go version and dependencies
 # This fixes vulnerabilities found in the pre-built Caddy images (e.g. CVE-2025-59530, stdlib issues)
-FROM --platform=$BUILDPLATFORM golang:1.23-alpine AS caddy-builder
+FROM --platform=$BUILDPLATFORM golang:1.25-alpine AS caddy-builder
 ARG TARGETOS
 ARG TARGETARCH
 ARG CADDY_VERSION

backend/go.mod

@@ -1,6 +1,6 @@
 module github.com/Wikid82/charon/backend
 
-go 1.23
+go 1.25
 
 require (
 	github.com/containrrr/shoutrrr v0.8.0

go.work

@@ -1,3 +1,3 @@
-go 1.23
+go 1.25
 
 use ./backend