feat(ci): add Gitea Actions workflow for auto-build on push

- Move build.sh to scripts/build.sh (convention from project-template)
- Add .gitea/workflows/build.yml: triggers on push to main when
  Dockerfile or config files change, builds :dev tag via Kaniko
- Every push → CI builds harbor.manabo.org/library/smtp-relay:dev
  → ArgoCD Image Updater detects new digest → deploys to hermes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -0,0 +1,23 @@
+name: Build smtp-relay
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'Dockerfile'
+      - 'entrypoint.sh'
+      - 'main.cf'
+      - 'master.cf'
+      - 'smtpd.conf'
+      - 'scripts/build.sh'
+      - '.gitea/workflows/build.yml'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: [self-hosted, valhalla]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build image (dev)
+        run: bash scripts/build.sh dev

scripts/build.sh

@@ -1,9 +1,9 @@
 #!/usr/bin/env bash
-# build.sh [tag]
-# Packages the smtp-relay context, uploads to MinIO, runs Kaniko in-cluster, waits.
+# scripts/build.sh [tag]
+# Empaqueta el contexto, sube a MinIO, lanza Kaniko en-cluster, espera.
 set -euo pipefail
 
-TAG="${1:-latest}"
+TAG="${1:-dev}"
 HARBOR="harbor.manabo.org"
 IMAGE="${HARBOR}/library/smtp-relay:${TAG}"
 BUCKET="kaniko-builds"
@@ -14,10 +14,13 @@ echo "==> Building ${IMAGE}"
 echo "==> Packaging context ..."
 tar -czf /tmp/kaniko-context.tar.gz \
   --exclude='.git' \
-  --exclude='build.sh' \
-  --exclude='k8s' \
-  -C "$(dirname "$0")" .
-echo "==> Uploading to MinIO (${BUCKET}/${CONTEXT_KEY}) ..."
+  --exclude='scripts' \
+  --exclude='.gitea' \
+  --exclude='README.md' \
+  -C "$(git rev-parse --show-toplevel)" \
+  Dockerfile entrypoint.sh main.cf master.cf smtpd.conf
+
+echo "==> Uploading to MinIO ..."
 mc cp /tmp/kaniko-context.tar.gz "minio/${BUCKET}/${CONTEXT_KEY}"
 rm /tmp/kaniko-context.tar.gz