fix(sepia): qualify the Fable 5 and Opus 5 instructions by release match

Codex round 3 on #46: the Fable 5 and Opus 5 prose tables declared
their embedded vendor instructions operative for the executor without
a release condition. Every Claude table loads for a known Claude
family, so an Opus 4.8 or unmatched Claude executor would have applied
the Fable-specific brevity instruction at full strength. Both cells now
use the same conditional form as the Fable 5.1 row: operative for a
role whose release matches the table's tag, a prior for any other
Claude release, with the author/executor handling stated per role.

Whole-file check before pushing: no remaining unconditional "is
operative" phrasing; the only operative mentions are the preamble's
definition and the three release-qualified cells.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TtoUEQarAYtQYrZLLwqjao