chore: upgrade Go to 1.26.3

Bump Go version from 1.26.2 to 1.26.3 across the project — go.mod,
goreleaser Dockerfiles for control-plane, CLI, and artifact-cas, and the
Key Technologies section in CLAUDE.md. Updates the golang Docker image
digest to sha256:2981696eed011d747340d7252620932677929cce7d2d539602f56a8d7e9b660b.

Assisted-by: Claude Code
Signed-off-by: Jose I. Paris <jiparis@chainloop.dev>

Author: jiparis

CLAUDE.md

@@ -135,7 +135,7 @@ make migration_lint         # Lint migration files
 
 ## Key Technologies
 
-- **Language**: Go 1.26.2
+- **Language**: Go 1.26.3
 - **API**: gRPC with HTTP/JSON gateway, Protocol Buffers with buf
 - **Database**: PostgreSQL with Ent ORM, Atlas for migrations
 - **Authentication**: OIDC, JWT tokens

app/artifact-cas/Dockerfile.goreleaser

@@ -1,4 +1,4 @@
-FROM golang:1.26.2@sha256:2a2b4b5791cea8ae09caecba7bad0bd9631def96e5fe362e4a5e67009fe4ae61 AS builder
+FROM golang:1.26.3@sha256:2981696eed011d747340d7252620932677929cce7d2d539602f56a8d7e9b660b AS builder
 
 FROM scratch
 

app/cli/Dockerfile.goreleaser

@@ -1,4 +1,4 @@
-FROM golang:1.26.2@sha256:2a2b4b5791cea8ae09caecba7bad0bd9631def96e5fe362e4a5e67009fe4ae61 AS builder
+FROM golang:1.26.3@sha256:2981696eed011d747340d7252620932677929cce7d2d539602f56a8d7e9b660b AS builder
 RUN mkdir -p /.config/chainloop
 
 FROM scratch

app/controlplane/Dockerfile.goreleaser

@@ -1,4 +1,4 @@
-FROM golang:1.26.2@sha256:2a2b4b5791cea8ae09caecba7bad0bd9631def96e5fe362e4a5e67009fe4ae61 AS builder
+FROM golang:1.26.3@sha256:2981696eed011d747340d7252620932677929cce7d2d539602f56a8d7e9b660b AS builder
 
 FROM scratch
 

go.mod

@@ -1,6 +1,6 @@
 module github.com/chainloop-dev/chainloop
 
-go 1.26.2
+go 1.26.3
 
 require (
 	cloud.google.com/go/secretmanager v1.16.0