Replace the old `void-exp` repository defaults with `void` so the Make targets,
registration helper, example config, verification messaging, and sample test
fixtures all line up with the new managed image name.
Keep the scope to repo-facing naming only: config overrides, helper output, and
test fixtures now expect `void`, while runtime compatibility for existing local
`void-exp` VMs remains an operational concern outside this commit.
Validation: go test ./..., make build, and a local `banger vm create --image void`
smoke boot with ssh and opencode ports up.
Hard-cut banger away from source-checkout runtime bundles as an implicit source of\nimage and host defaults. Managed images now own their full boot set,\nimage build starts from an existing registered image, and daemon startup\nno longer synthesizes a default image from host paths.\n\nResolve Firecracker from PATH or firecracker_bin, make SSH keys config-owned\nwith an auto-managed XDG default, replace the external name generator and\npackage manifests with Go code, and keep the vsock helper as a companion\nbinary instead of a user-managed runtime asset.\n\nUpdate the manual scripts, web/CLI forms, config surface, and docs around\nthe new build/manual flow and explicit image registration semantics.\n\nValidation: GOCACHE=/tmp/banger-gocache go test ./..., bash -n scripts/*.sh,\nand make build.
Separate tracked source from generated artifacts so the repo root stops accumulating helper scripts, manifests, and local runtime outputs.
Move manual shell entrypoints under scripts/, manifests under config/, and the Firecracker API reference under docs/reference/. Make build and runtimebundle now target build/bin, build/runtime, and build/dist as the canonical source-checkout paths.
Update runtime discovery, helper scripts, tests, and docs to follow the new layout while keeping legacy source-checkout runtime fallbacks for existing local bundles during migration.
Validated with bash -n on the moved scripts, make build, and GOCACHE=/tmp/banger-gocache go test ./....
