v0.5.4

The documentation cleanup; released because the walkthrough, PRIVACY.md and
a setting's description ship inside the package.

Changed

• A documentation cleanup against the code: the walkthrough says dictation
  is a Windows and macOS feature; PRIVACY.md says the panel lists models
  when it opens while signed in, that the extension only checks whether
  the CLI's credential file exists, and that Sign out and /logout are
  one action; SECURITY.md describes the machine-scoped settings and the
  two backends' shell commands as they are; AGENTS.md, CONTRIBUTING.md,
  CLAUDE.md, .env.example, the knip comment and two script headers no
  longer describe the key injection removed in 0.1.0, a CI matrix that
  never existed or an interface that does not; the autosave setting's
  description matches what it does; PLAN.md's architecture diagram, gates
  table, open questions, budgets and milestone notes are brought up to
  date, with a register row for the test-only Selection casts. The
  certification folder gains an index, the harness keeps its Chrome
  profile in a temporary directory, and the Claude Code reference
  screenshots left the repository.