Fix Alpine bootstrap and add agent VM workflows

[Vbitz]

Summary

• initialize AGENTS.star with Git, Go, GitHub, build/test, named VM, image pull, guest exec, and guarded PR workflows
• make build directory creation recursive/idempotent and let cc create its private cache
• redirect auto-started daemon diagnostics to the cache's ccvm.log so captured CLI output closes promptly
• distinguish package transfer completion from complete kernel preparation, including cached success
• avoid repeated HTTP WriteHeader calls during progress streaming
• add regression tests and document daemon logging

Validation

• configuration syntax validation passed
• go test -race -short ./cmd/cc ./internal/kernel/alpine ./internal/ccvmd ./client -count=1 -timeout 3m
• go vet ./cmd/cc ./internal/kernel/alpine ./internal/ccvmd ./client
• Go formatting checks passed
• fresh-cache Linux/amd64 KVM smoke test: daemon auto-start, cold and cached doctor, local Alpine image import, VM boot, guest commands and file write/read, clean VM shutdown and daemon shutdown

The smoke test used no guest networking or host shares. No downloaded artifacts or cache files are included.