fix(rpm): own app/runtime dirs so the jpackage launcher finds its .cfg

[kdroidFilter]

Problem

Installing the RPM on Fedora/RHEL and launching the app fails with:

Error opening "NucleusDemo.cfg" file: No such file or directory

(issue #251)

Root cause

electron-builder builds RPMs via fpm, which lists only files and never emits %dir entries for the app's own directory tree. The jpackage launcher (libapplauncher.so, Package.cpp::initAppLauncher) discovers the app and runtime directories by running rpm -ql <pkg> and matching lines that endsWith /app and /runtime:

// RPM: "rpm -ql '" + name + "'"
if (tstrings::endsWith(line, "/app"))     { appDir = line; }
if (tstrings::endsWith(line, "/runtime")) { runtimeDir = line; }

With no directory entries, those scans return nothing → appDir/runtimeDir stay empty → the launcher can't resolve its .cfg. DEB was never affected because dpkg -L already lists directories.

Fix

Pass fpm's --rpm-auto-add-directories in the generated electron-builder rpm: config so fpm owns every payload directory (while still excluding the standard filesystem-package dirs via its bundled filesystem_list), mirroring what jpackage's own template.spec does with comm -23 against the filesystem package.

rpm:
  fpm:
    - "--rpm-auto-add-directories"

This replaces the heavyweight approach in #363 (extract + rebuild the RPM via rpmbuild) with a single, correct flag.

Verified

Reproduced with the exact fpm binary electron-builder caches:

• Before: rpm -qlp lists only files — no /app or /runtime directory entries.
• After: rpm -qlp lists …/lib/app and …/lib/runtime directory entries → launcher resolves the .cfg.
• Filesystem-package dirs (/opt, /usr, /usr/bin, /usr/share, /usr/share/applications, /usr/share/icons) are correctly excluded — no conflict with the filesystem package.
• Only co-owns /usr/share/icons/hicolor/*, which is safe (rpm reference-counts directory ownership; only differing regular files conflict).

Launcher behavior confirmed against OpenJDK Package.cpp and the built libapplauncher.so (contains rpm -ql ', dpkg -L ', tstrings::endsWith).

Tests

Adds ElectronBuilderRpmConfigTest — the RPM config emits the flag, it coexists with rpm.depends, and the DEB config does not emit the rpm-only flag.

Note

Addresses the launcher .cfg error in #251. The separate "installer downloaded the RPM but failed to install" symptom in that issue is unrelated to %dir entries (it's a silent-failure bug in the nucleus-website install script + missing demo assets on some releases) and is handled separately.