Add Cloud Agent dev environment for kernel build + QEMU boot

[PatrisiousHaddad]

Summary

Sets up a Cursor Cloud Agent development environment for this Linux kernel tree so agents can build the kernel and boot it end-to-end.

• .cursor/environment.json — declares the environment and its install command.
• .cursor/install.sh — idempotent bootstrap: installs the kernel build toolchain (build-essential, bc, bison, flex, libssl-dev, libelf-dev, libncurses-dev, cpio, kmod, dwarves, rsync) plus qemu-system-x86 and busybox-static, generates .config via make defconfig (only if absent), and builds arch/x86/boot/bzImage.

Files are force-added because the kernel .gitignore ignores all dotfiles (.*).

Validation

• make defconfig + make -j8 bzImage build succeeds (Kernel: arch/x86/boot/bzImage is ready).
• Booted the freshly built kernel in QEMU with a minimal busybox initramfs; userspace init ran, printed uname -a / /proc/version (Linux version 7.1.0-rc7-...), and powered down cleanly.
• Install command is idempotent (second run is a fast incremental no-op).