fix(snapshots): Show clear error when project slug was renamed

[NicoHinderling]

snapshots upload against a renamed project slug failed with could not parse JSON response: missing field 'objectstore'. On a rename the API returns a 302 whose body the snapshot calls deserialized as their response type, bypassing convert_rnf — the helper every other project-scoped endpoint uses to surface renames.

This routes both snapshot calls through convert_rnf, which now reads the new slug from the top-level slug field the server actually sends (it previously read a non-existent detail.slug, leaving the rename message dead for all ProjectNotFound callers). Users now get the existing clear project was renamed to '<slug>' error.

Scope is project renames only; org renames (404) and the same latent failure on events list / issues commands are out of scope.

Fixes #3337