Add production .rpm packaging and dnf setup; share runtime staging

Phase 3 of the improvement plan (PR 9 of the sequence): the dnf/Fedora
packaging half, in separate Linux-specific files, mirroring the apt/.deb work.

- packaging/linux/common/stage-runtime.sh: shared runtime-only payload staging
  extracted from the .deb builder so the two package formats never drift. It
  copies app code + a fixed Electron runtime + production npm deps (npm ls
  --omit=dev), guards against dev-dep leaks, and fails without node_modules.
  The .deb builder now delegates to it.
- packaging/linux/fedora/stepforge.spec: runtime Requires (nss, nspr, gtk3,
  …), Recommends (xinput, portal, pipewire), %license, and a %post that makes
  chrome-sandbox setuid and refreshes desktop/MIME/icon caches. No compilation
  — it packages the prebuilt BuildRoot.
- packaging/linux/fedora/package.sh: stages the shared payload, substitutes
  version/maintainer into the spec, and runs rpmbuild against the prebuilt
  BuildRoot with detected arch. Requires rpmbuild + node_modules; emits an
  .rpm + sha256.
- scripts/linux/dnf/install-runtime-deps.sh and install-build-deps.sh:
  separate runtime vs build dependency sets for dnf (runtime installs no build
  tools).
- docs/linux/dnf.md: Fedora/RHEL install + build guide, distinct from apt.md.

Tests: packaging-linux.test.js gains Fedora/dnf structural checks (spec
Requires + MPL-2.0 + %license + sandbox setup, builder shares staging +
requires rpmbuild, dnf build/runtime dep separation, shared staging never
copies the whole dev tree). tests/integration/linux/package-rpm.test.sh builds
a real .rpm and asserts runtime-only contents (honest skip when rpmbuild is
absent, as on this apt host).

Verified: 13 packaging unit tests pass; the refactored .deb builder still
produces a valid runtime-only package (integration test green); the .rpm
integration test skips cleanly where rpmbuild is unavailable.

Co-Authored-By: Claude Fable 5 <[email protected]>

scripts/linux/dnf/install-runtime-deps.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Install the RUNTIME libraries StepForge needs on dnf-based systems (Fedora,
+# RHEL/derivatives). These are the shared libraries the packaged Electron
+# runtime links against, plus the X11/portal integration used for capture.
+# For END USERS installing from the tarball; the .rpm declares the same set as
+# Requires so dnf pulls them automatically.
+set -euo pipefail
+
+if ! command -v dnf >/dev/null 2>&1; then
+  echo "This script is for dnf-based systems (Fedora/RHEL). Use the apt script on Debian/Ubuntu." >&2
+  exit 1
+fi
+
+SUDO=""
+if [ "$(id -u)" -ne 0 ]; then SUDO="sudo"; fi
+
+PACKAGES=(
+  # Chromium/Electron shared libraries
+  nss nspr atk at-spi2-atk at-spi2-core cups-libs libdrm
+  gtk3 mesa-libgbm alsa-lib libxkbcommon
+  libXcomposite libXdamage libXfixes libXrandr libxshmfence
+  # X11 per-click capture (marker-accurate) — X11 sessions only
+  xorg-x11-server-utils xinput
+  # Wayland screen-share via the XDG portal + PipeWire
+  xdg-desktop-portal pipewire
+)
+
+echo "Installing StepForge runtime dependencies via dnf..."
+# Some package names differ across Fedora releases; install best-effort so one
+# missing optional name doesn't abort the whole set.
+$SUDO dnf install -y "${PACKAGES[@]}" || {
+  echo "Some packages were unavailable; retrying individually..." >&2
+  for pkg in "${PACKAGES[@]}"; do $SUDO dnf install -y "$pkg" || echo "  (skipped: $pkg)" >&2; done
+}
+echo "Done. StepForge runtime dependencies are installed."