Fix inverted changelog area key/title mapping

[Copilot]

The changelog checker and parser were treating / as the canonical area key and decoding ~ from entry filenames before lookup. Envoy’s changelog config does the opposite: keys are filename-safe ids using ~, titles are display strings using /, and filenames use the key verbatim.

• Checker: restore canonical key handling

  • Accept ~ in area keys and reject / in keys.
  • Accept / in titles and reject ~ in titles via title validation.
  • Validate entry filename areas against the key regex and look them up directly in self.areas.
  • Remove the inverted checks that treated ~ as filename-only escaping and required slash keys to carry special title handling.

• Base utils: preserve entry area keys

  • Revert filename-area decoding in data_from_entry_map.
  • Remove the AREA_SEPARATOR / AREA_FILENAME_SEPARATOR helpers and conversion functions added for the inverted model.

• Docs and tests

  • Rewrite the README section to describe the actual contract:
    • YAML keys use ~
    • titles use /
    • entry filenames use the key unchanged
  • Update tests to cover valid dns~cares keys, invalid dns/cares keys, invalid dns~cares titles, direct filename-key matching, and unchanged parsed entry areas.

areas:
  dns~cares:
    title: dns/cares

changelogs/current/new_features/dns~cares__preserve-qid.rst