chore: release v26.21.0

bump debian image version

fix: inject version from tag into goreleaser builds

The ldflags were missing {{.Version}}, so release binaries always
showed "dev" instead of the actual tag version.

refactor: rename ephemeral containers to volume-exposer and speed up …

…demos

Rename all nfs-ganesha container names to volume-exposer so users
don't see internal implementation details. Also remove redundant
"-ephemeral-" from SSH container names. Increase demo typing speed
from 150ms to 120ms.

feat: add --version flag, update help text for NFS, fix VHS sudo

- Add pkg/version package with ldflags-set version (goreleaser compatible)
- Set rootCmd.Version so cobra handles --version automatically
- Update CLI help text to mention both SSHFS and NFS-Ganesha backends
- Fix VHS workflow: copy kubeconfig to /root/.kube instead of running
  vhs as root (which breaks Chromium)
- Add ldflags to Makefile bin target for local dev builds
- Regenerate docs

docs: update krew plugin description to mention NFS backend

bump go in golint

bump debian image

bump go debian

bump go debian