feat(emacs): robust Nix-based Emacs setup with daemon service, improved elisp dev, and full package documentation

- Emacs daemon runs as a systemd service via Nix
- Modular Emacs config with Nix-managed packages (elisp-slime-nav, aggressive-indent, highlight-defined, etc.)
- Keybinding fixes and error handling improvements
- New EMACS_README.md explains ecosystem and troubleshooting
- Nix config: GUI sudo askpass, podman, and desktop tweaks
- All errors from missing packages and keybindings resolved

machines/little-rascal/configuration.nix

@@ -34,9 +34,7 @@
     ../../modules/users/shell-aliases.nix
 
     # Virtualization
-    # ../../modules/virtualization/libvirt.nix
-    # ../../modules/virtualization/incus.nix
-    # ../../modules/virtualization/podman.nix
+    ../../modules/virtualization/podman.nix
 
     # Audio
     ../../modules/sound/pipewire.nix