Add dev/self-hosting packages: qemu, neovim, build tools

14 new packages in extra/:
- qemu-9.2.3, edk2-ovmf-202411 (QEMU + UEFI firmware for testing)
- squashfs-tools-4.6.1, xorriso-1.5.7, mtools-4.0.48 (ISO building)
- efibootmgr-18, efivar-39 (UEFI boot management)
- rsync-3.4.1, lz4-1.10.0, nasm-2.16.03 (build/transfer tools)
- neovim-0.11.1, htop-3.4.0, tmux-3.5a, libevent-2.1.12 (dev tools)

Total: 138 packages (67 core, 40 extra, 19 desktop, 12 gaming)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

extra/libevent/libevent.toml

@@ -0,0 +1,20 @@
+[package]
+name = "libevent"
+version = "2.1.12"
+description = "Event notification library"
+url = "https://libevent.org/"
+license = "BSD-3-Clause"
+
+[source]
+url = "https://github.com/libevent/libevent/releases/download/release-${version}-stable/libevent-${version}-stable.tar.gz"
+sha256 = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+
+[dependencies]
+run = ["glibc", "openssl"]
+build = ["gcc", "make"]
+
+[build]
+system = "autotools"
+configure = """./configure --prefix=/usr --disable-static"""
+make = """make"""
+install = """make DESTDIR=${PKG} install"""