feat(ci): Add Fedora RPM package build workflow

Following PR #950 which introduced the RPM spec and systemd unit files,
this adds a comprehensive CI workflow for building, signing, testing, and
publishing RPM packages. Includes GPG signing infrastructure with Ed25519
keys and automatic package registry deployment for stable, development,
and feature branch builds.

Add documentation for RPM installation methods, repository configuration,
and package management. Fix linting issues in spec file for pre-commit
compliance.

fedora/RPM-GPG-KEY-continuwuity.asc

@@ -0,0 +1,16 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=dxDr
+-----END PGP PUBLIC KEY BLOCK-----

fedora/continuwuity.spec.rpkg

@@ -1,6 +1,5 @@
-# This should be run using rpkg-util: https://docs.pagure.org/rpkg-util
+# This should be run using rpkg: https://docs.pagure.org/rpkg
 # it requires Internet access and is not suitable for Fedora main repos
-# TODO: rpkg-util is no longer maintained, find a replacement
 
 Name:           continuwuity
 Version:        {{{ git_repo_version }}}