refactor(cli): isolate platform internals

[Episkey-G]

Summary

• Move legacy platform runtime code from top-level base into cmd/internal/platform and remove top-level base, ux, and ansi packages.
• Move ANSI helpers into pkg/ui and keep product-facing contracts in pkg/cli/pkg/ui.
• Preserve products/ production code unchanged while tightening hack/check-product and runtime guard tests against legacy imports.
• Fix api --repeats failure handling so failures include error detail and return a non-zero exit code.

Validation

• go test ./...
• go vet ./...
• make build
• go run ./hack/gen-products
• go test ./hack/snapshot -count=1
• go test ./hack/check-product -count=1
• go run ./hack/check-product
• git diff --exit-code -- products
• test ! -d base && test ! -d ux && test ! -d ansi
• rg 'github.com/ucloud/ucloud-cli/(base|ux|ansi)' --glob '!docs/**' --glob '!TODOS.md' returned no matches
• rg 'github.com/ucloud/ucloud-cli/(base|ux|ansi|cmd/internal)' products --glob '!**/*_test.go' returned no matches

E2E already verified on this branch

• UHost live lifecycle create/delete cleanup passed.
• ULHost repeat create cleanup passed.
• OAuth refresh + Bearer API project list passed.
• OAuth auth login --no-browser localhost callback flow passed.
• Negative api --repeats ULHost create with invalid params returned rc=1, printed API error detail, and follow-up DescribeULHostInstance returned TotalCount=0.

Notes

• products/ code is intentionally unchanged.
• The historical --profile=... / -p ... early-parse inconsistency is intentionally deferred and not part of this PR.
• Local untracked docs/TODOS drafts were not committed.