v0.5.0 — DevEx Charter

Source change: PR #35. First release under the DevEx Charter name. This is a pre-1.0
identifier break: installed join-the-team plugins do not update to it automatically.

Changed

• Rebrand the plugin as DevEx Charter (devex-charter) across portable,
  Claude, Kimi and Gemini manifests, commands, README and installation guidance
  (#34).
  Keep the repository, legacy marketplace identifier and orientation environment
  variable stable. Follow the migration guide; live host
  migration and upstream directory listings are separate, unverified gates.
• Plan the paired harness delivery benchmark and coordination pilot; no runtime change.