AppRC 0.26.0

💥 Breaking changes

• Breaking: Saved secret=True fields now use the user or storage layer's
  .secret.env companion, and AppRC blocks secret saves in shared directories.
  Affected: Applications or scripts that read secret assignments directly
  from apprc.user.env or apprc.storage.env, or save them in a shared
  storage root.
  Migration: Read fields through AppRC.resolve(); run
  config secrets migrate --scope user|storage for old assignments, then
  choose a private root or run config secrets repair after reviewing its
  permission change.

➕ Added

• Added apprc-gui, a separate Toga settings view that applications can
  embed in their own desktop window for setup and editing.
• Added private user and storage secret companions, explicit migration and
  permission repair commands, and doctor guidance for unsafe files.
• Added cross-process locks for managed edits and a Windows MSI installer
  guide for applications using AppRC.

💔 Changed

• Storage archives exclude apprc.storage.secret.env and refuse legacy
  secret assignments in apprc.storage.env; restore creates an empty
  companion. Purge removes secret companions with other managed files.