Refactor AWF helper monolith into focused modules with preserved command/env APIs

[Copilot]

pkg/workflow/awf_helpers.go had become the largest non-test source file, with command assembly and feature/env/image/ARC-DinD helpers co-located. This change decomposes that surface into focused files while keeping behavior and exported interfaces stable.

• Module split by responsibility

  • awf_command.go: BuildAWFCommand, BuildAWFArgs, GetAWFCommandPrefix, WrapCommandInShell
  • awf_arcdind.go: ARC/DinD topology detection and chroot/workflow-call network patch helpers
  • awf_feature_support.go: AWF version-gated capability checks (awfSupports*, awfVersionAtLeast)
  • awf_env.go: environment assembly/injection helpers (ComputeAWFExcludeEnvVarNames, token/max-credit env wiring)
  • awf_image.go: image tag+digest resolution and model JSON path export script helpers

• Public API and behavior preserved

  • Kept exported entrypoints unchanged:
    • BuildAWFCommand
    • BuildAWFArgs
    • GetAWFCommandPrefix
    • WrapCommandInShell
    • ComputeAWFExcludeEnvVarNames
  • No interface or call-site contract changes; refactor is structural and boundary-oriented.

• Test boundary alignment

  • Existing AWF helper coverage remains intact while logic is reorganized around clearer module boundaries (command assembly vs feature gates vs ARC/DinD vs env vs image).

// command assembly API remains stable after split
cmd, err := BuildAWFCommand(cfg, wfData, fwConfig)
if err != nil {
    return err
}
args := BuildAWFArgs(cfg, wfData, fwConfig)
_ = append([]string{cmd}, args...)

• Fixes [file-diet] File Diet: Refactor pkg/workflow/awf_helpers.go (1148 lines) #50263