sic: add sicd + sic-agent packages (Arch + Debian) + CI

sicd (daemon, target hosts) and sic-agent (client + agent skills) from
git.reauktion.de/marfrit/sic v0.1.0. Go binaries, cross-built with GOARCH.

- arch/sicd, arch/sic-agent: PKGBUILDs (build from source via go).
- debian/sicd, debian/sic-agent: control/copyright/changelog + build-deb.sh
  (per-arch amd64/arm64).
- .gitea/workflows/build.yml: 4 jobs — Arch aarch64 (repo-signed, -> nc) and
  Debian amd64+arm64 (-> hertz reprepro, bookworm+trixie). continue-on-error,
  chained after the existing jobs.

Validated locally: Arch aarch64 pkgs + Debian arm64/amd64 debs build; the
packaged sicd binary runs (netstring exec).

arch/sic-agent/PKGBUILD

@@ -0,0 +1,35 @@
+# Maintainer: Markus Fritsche <mfritsche@reauktion.de>
+# sic client + agent skills. For agent hosts that drive remote commands.
+# Source of truth: git.reauktion.de/marfrit/sic
+
+pkgname=sic-agent
+pkgver=0.1.0
+pkgrel=1
+pkgdesc="sic client + agent skills: frame argv as netstrings and run it on a remote host via sicd (foreground + background skills)"
+arch=('x86_64' 'aarch64')
+url="https://git.reauktion.de/marfrit/sic"
+license=('MIT')
+makedepends=('go')
+depends=('openssh')
+source=("sic-${pkgver}.tar.gz::https://git.reauktion.de/marfrit/sic/archive/v${pkgver}.tar.gz")
+sha256sums=('5cd10c3a1ab7361e72e7579af5819f9d322ecd59424541cfb80e5b7514253511')
+
+build() {
+    cd "${srcdir}/sic"
+    case "$CARCH" in
+        x86_64)  export GOARCH=amd64 ;;
+        aarch64) export GOARCH=arm64 ;;
+    esac
+    export GOOS=linux CGO_ENABLED=0 GOFLAGS='-buildvcs=false -trimpath'
+    go build -ldflags='-s -w' -o sic ./cmd/sic
+}
+
+package() {
+    cd "${srcdir}/sic"
+    install -Dm755 sic          "${pkgdir}/usr/bin/sic"
+    # Agent skills — link into the agent's skills dir (e.g. ~/.claude/skills/).
+    install -Dm644 SKILL.md     "${pkgdir}/usr/share/sic-agent/skills/sic/SKILL.md"
+    install -Dm644 SKILL-bg.md  "${pkgdir}/usr/share/sic-agent/skills/sic-bg/SKILL.md"
+    install -Dm644 README.md    "${pkgdir}/usr/share/doc/${pkgname}/README.md"
+    install -Dm644 LICENSE      "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
+}