Keep vmsh and daemon frontends in experimental cc

[Vbitz]

The production desktop apps are moving to an independent, reduced in-process runtime. This PR keeps the experimental runtime, full daemon/worker system, and shell frontends together in cc.

• Move the interactive vmsh frontend, vmsh-call, shell/daemon packages, behavioral tests, and protocol documentation into frontends/vmsh. Its local module uses this cc checkout directly.
• Preserve the session-oriented host/VM/SSH shell and bundled daemon entry point. Add shell builds to the existing build script and a manual experimental release workflow; shell upgrades use cc releases.
• Remove the old Python frontend, wheel publishing, and scripts that require that frontend. A future production Python API is separate work.
• Add one short shell CI job. Keep expensive KVM/rootfs suites available through manual workflow dispatch rather than on every commit.

Validation: built guest init payloads; go test -short ./... -count=1 -timeout 3m and go vet ./... pass in frontends/vmsh; shell and workflow syntax checks and git diff --check pass. The existing cc runtime and daemon implementation are unchanged.

Part of tinyrange/crumblecracker#270. The production repository remains tinyrange/vmsh pending its separate CrumbleCracker rename; no automatic synchronization or compatibility policy is introduced.

Companion production PR: tinyrange/crumblecracker#271