playbooks: add a Sonnet 5.5 adaptation chapter when Sonnet 5.5 ships #4347

Problem

Sonnet 5.5 is expected in the coming weeks. Until a sonnet-5-5.md chapter exists, meta-rule 3 in playbooks:fable-5 sends Sonnet 5.5 sessions to sonnet-5.md and applies only its method, not its model-specific calibration.

Done when

• plugins/playbooks/reference/model-adaptation/sonnet-5-5.md exists. It is sourced from the official Sonnet 5.5 prompting guide, the what's-new page, and any usage guide, and it follows the verbatim-quotation rules in that directory's AGENTS.md.
• Sonnet 5.5 appears in meta-rule 3's chapter list, in the fable-5 skill description, and in a trigger eval.
• The design section of sonnet-5.md (propose options) and its effort-scale claims have been rechecked against the 5.5 guide. Anything that is reversed is recorded in the new chapter.
• The model-config fallback section has been checked for Sonnet classifiers. Today the refusals page lists classifiers only for Fable and Opus.

Trigger

Sonnet 5.5 is released.