AppRC 0.21.0

💥 Breaking changes

• Breaking: config storage add and config storage repoint now reject a
  resolved root already registered under another live name.
  Affected: Users intentionally creating multiple aliases for one storage
  directory.
  Migration: Keep one name for each root, or point each name at a distinct
  directory. Existing alias registries remain readable and config doctor
  reports the ambiguity.

➕ Added

• Added filesystem paths as runtime selectors for both --storage and
  <APP>_STORAGE. Relative paths resolve from apprc.toml; initialized
  unregistered paths work without registry writes, and interactive CLIs can
  register them under a user-approved name.
• Added a three-way first-run choice for the default directory, a custom
  directory with cross-platform path completion, or cancellation.
• Added storage_selector_kind to bootstrap results and
  selected_storage_selector_kind to doctor and paths JSON.

💔 Changed

• Changed runtime storage readiness to require an existing directory with a
  readable apprc.storage.env. Error messages now include the failed path
  and exact setup command.
• Changed config edit to open in repair mode when selection, registry, or
  storage readiness is invalid. Setup remains enabled while uninitialized
  storage fields remain disabled.

🔨 Fixed

• Fixed repeated bootstrap so unchanged values written by the prior AppRC
  run are removed before reload while caller mutations are preserved; failed
  reloads restore the prior successful process state.
• Fixed Textual duplicate registration and archive restoration. Duplicate
  names are rejected before extraction, and archive installation, registry
  registration, and archive-row cleanup now roll back together.