Add a Linux riscv64 release build (deb, rpm, tar.gz) (#102)

* Add Linux riscv64 release build and switch runners to Ubuntu 26.04

- release.yml: new linux-riscv64 job cross-compiled on ubuntu-26.04 against
  ports.ubuntu.com riscv64 libs, tar.gz only, artcraft-launcher --version
  smoke-tested under QEMU. Updated flatpak runner matrix to ubuntu-26.04.
  Draft-release job now requires linux-riscv64 and checks the tarball.
- packaging/linux/package.sh: CROSS_ARCH / CROSS_TARGET / CROSS_COMPILE / EMULATOR support.
- platform.rs: add Arch::Riscv64 variant, map linux-riscv64 token, and prioritize
  tarball format for riscv64 on Linux.
- web.rs: detect riscv64 architecture in visitor user agent.
- README and AGENTS.md: document the riscv64 tarball.

* linux: build deb and rpm packages for riscv64

* ci: configure actionlint to recognize ubuntu-26.04 runner labels

* Keep riscv64 and Flatpak release jobs on Ubuntu 24.04

24.04 is what PhotoCraft's linux-riscv64 job uses, so the riscv64 binaries
need glibc 2.39 (as the README says) rather than 26.04's newer glibc, and
the release pipeline keeps runner images it has already proven on. Drop the
actionlint label config that 26.04 needed, revert the default_kinds and
download_kinds matches to match on the OS alone, simplify the riscv UA check,
and rustfmt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Brandon Thomas <echelon@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -335,9 +335,75 @@ jobs:
           path: dist/release/*
           if-no-files-found: error
 
+  linux-riscv64:
+    name: Linux riscv64
+    needs: version
+    # Cross-compiled on x86_64 (no hosted RISC-V runners) against the runner's own Ubuntu release
+    # from ports.ubuntu.com, so the binaries need that release's glibc (24.04: 2.39). 22.04's
+    # riscv64 ports lag its amd64 updates, which breaks the multiarch install. deb, rpm, and
+    # tar.gz; artcraft-launcher --version is smoke-tested under QEMU. Follows PhotoCraft's job.
+    runs-on: ubuntu-24.04
+    # No `environment: release`: this job reads no secrets, so a branch dry run can run it.
+    env:
+      ARTCRAFT_LAUNCHER_VERSION: ${{ needs.version.outputs.version }}
+      ARTCRAFT_LAUNCHER_BUILD_DATE: ${{ needs.version.outputs.date }}
+      NFPM_VERSION: 2.47.0
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: riscv64gc-unknown-linux-gnu
+      - uses: Swatinem/rust-cache@v2
+        with:
+          key: release-linux-riscv64
+      - name: Apply version override
+        if: inputs.version != ''
+        run: cargo xtask version set "$ARTCRAFT_LAUNCHER_VERSION"
+      - name: Install cross-compilation dependencies
+        run: |
+          . /etc/os-release
+          sudo dpkg --add-architecture riscv64
+          # Pin the existing (archive.ubuntu.com) sources to amd64; riscv64 comes from ports.
+          if [ -f /etc/apt/sources.list.d/ubuntu.sources ]; then
+            sudo sed -i '/^Types: deb/a Architectures: amd64' /etc/apt/sources.list.d/ubuntu.sources
+          fi
+          if [ -f /etc/apt/sources.list ]; then
+            sudo sed -i 's/^deb /deb [arch=amd64] /g' /etc/apt/sources.list
+            sudo sed -i 's/^deb-src /deb-src [arch=amd64] /g' /etc/apt/sources.list
+          fi
+          for suite in "$VERSION_CODENAME" "$VERSION_CODENAME-updates" "$VERSION_CODENAME-security"; do
+            echo "deb [arch=riscv64] http://ports.ubuntu.com/ubuntu-ports $suite main universe restricted multiverse"
+          done | sudo tee /etc/apt/sources.list.d/riscv64.list
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            gcc-riscv64-linux-gnu binutils-riscv64-linux-gnu libc6-dev-riscv64-cross libc6-dev:riscv64 qemu-user \
+            libxkbcommon-dev:riscv64 libwayland-dev:riscv64 libx11-dev:riscv64 libxrandr-dev:riscv64 \
+            libxi-dev:riscv64 libgl1-mesa-dev:riscv64 \
+            desktop-file-utils appstream
+          curl -fsSL -o "$RUNNER_TEMP/nfpm.deb" \
+            "https://github.com/goreleaser/nfpm/releases/download/v${NFPM_VERSION}/nfpm_${NFPM_VERSION}_amd64.deb"
+          sudo dpkg -i "$RUNNER_TEMP/nfpm.deb"
+      - name: Build and package (deb, rpm, tar.gz)
+        env:
+          CARGO_TARGET_RISCV64GC_UNKNOWN_LINUX_GNU_LINKER: riscv64-linux-gnu-gcc
+          PKG_CONFIG_SYSROOT_DIR: /
+          PKG_CONFIG_PATH: /usr/lib/riscv64-linux-gnu/pkgconfig:/usr/share/pkgconfig
+          PKG_CONFIG_ALLOW_CROSS: "1"
+          CROSS_ARCH: riscv64
+          CROSS_TARGET: riscv64gc-unknown-linux-gnu
+          CROSS_COMPILE: riscv64-linux-gnu-
+          EMULATOR: qemu-riscv64
+          QEMU_LD_PREFIX: /usr/riscv64-linux-gnu
+        run: packaging/linux/package.sh --formats "deb rpm tar"
+      - uses: actions/upload-artifact@v4
+        with:
+          name: release-linux-riscv64
+          path: dist/release/*
+          if-no-files-found: error
+
   release:
     name: Draft GitHub Release
-    needs: [version, macos, windows, linux, flatpak, freebsd, web]
+    needs: [version, macos, windows, linux, linux-riscv64, flatpak, freebsd, web]
     runs-on: ubuntu-latest
     environment: release
     permissions:
@@ -364,8 +430,13 @@ jobs:
           for a in x64 x86 arm64; do
             expected+=("artcraft-launcher-$VERSION-windows-$a.msi" "artcraft-launcher-$VERSION-windows-$a-portable.zip")
           done
+          for a in x86_64 aarch64 riscv64; do
+            for ext in deb rpm tar.gz; do
+              expected+=("artcraft-launcher-$VERSION-linux-$a.$ext")
+            done
+          done
           for a in x86_64 aarch64; do
-            for ext in AppImage AppImage.zsync deb rpm tar.gz flatpak; do
+            for ext in AppImage AppImage.zsync flatpak; do
               expected+=("artcraft-launcher-$VERSION-linux-$a.$ext")
             done
           done