Prevent partial VM startup failures from leaking loop devices and dm state on the host.
Move root snapshot setup into a rollback-safe helper that records loop and mapper handles incrementally, tears them down in reverse order on failure, and reuses the same dm/loop cleanup path during normal runtime teardown. Also switch the daemon runner field to a small command-runner interface so the snapshot path can be tested with injected failures.
Add failure-injection coverage for losetup, blockdev, dmsetup, partial teardown, and joined rollback errors. Validated with go test ./... and make build.
Replace the shell-only user workflow with `banger` and `bangerd`: Cobra commands, XDG/SQLite-backed state, managed VM and image lifecycle, and a Bubble Tea TUI for browsing and operating VMs.\n\nKeep Firecracker orchestration behind the daemon so VM specs become persistent objects, and add repo entrypoints for building, installing, and documenting the new flow while still delegating rootfs customization to the existing shell tooling.\n\nHarden the control plane around real usage by reclaiming Firecracker API sockets for the user, restarting stale daemons after rebuilds, and returning the correct `vm.create` payload so the CLI and TUI creation flow work reliably.\n\nValidation: `go test ./...`, `make build`, and a host-side smoke test with `./banger vm create --name codex-smoke`.
