dispatch and apply_commands returned English prose that became the reply
subject, so the pure layers owned author-facing copy. They now return
reason::Reason and the mail-building edge resolves it through the catalogue.
core::rules needed no change: RuleError was already a typed enum, and its
Display stays for author-side tools. The daemon maps the variants itself
rather than borrowing that prose.
Error-path tests now assert on variants, so rewording main.ftl cannot break
them, and PruneModeUnknown carries the value the author actually sent.
Reason::every_variant_resolves_to_copy walks the enum, so a variant added
without a catalogue entry fails in tests rather than mailing someone
"???reason-…???".
Ports carrier's src/i18n.rs and its locales/en-US/main.ftl layout, same
fluent-bundle and unic-langid versions, so the two catalogues stay portable
between them. Only mail the daemon sends an author moves; operator CLI output
stays inline, since the operator runs the binary and reads English.
The error-reply reasons from dispatch and ApplyError are deliberately left
behind: dispatch is pure by contract, so those become reason identifiers
resolved at the mail-building edge in a separate change rather than having the
pure layer reach for a bundle.
Adds a test carrier lacks. FluentResource::try_new and add_resource both panic
on a malformed or duplicate-id catalogue, and nothing touches the bundle until
the daemon first mails someone, so without it a bad catalogue surfaces inside
poll() on a live instance.
Sentences are verbatim; the bodies are now hard-wrapped where they were single
long lines, which reads better in a plain-text client.
