docs: fix the false pinned-agents effort claim in plugin-philosophy #7099

Problem

Two stale records turned up during the Claude Haiku 5.5 release sweep and are outside that sweep's scope:

1. docs/plugin-philosophy.md, the pinned-agents record (as-of 2026-10-02, trigger "next model release"), says every named agent in this repository pins its effort. That is false. git grep -L '^effort:' -- 'plugins/*/agents/*.md' lists 11 agents with no effort pin: discovery docs-fetcher and sweep-worker; docs-hygiene compare-labeler; multi-agent docs-fetcher, drift-checker and drift-reader; review lane-verifier and stage-normalizer; testing green-fixer, green-runner and green-verifier. The trigger has fired, but the record cannot be re-dated while its claim is false.
2. (Withdrawn: #latest-models-comparison is the live id on the rendered models-overview page. compare-models is only the raw markdown heading slug. The two links that wrongly moved to #compare-models are restored in the playbooks Haiku 5.5 chapter PR.)

Proposed fix

• Scope the pinned-agents claim to the agents it is true for (for example, the agents skills dispatch through the Agent tool), or pin effort on the 11 agents. Then re-date the record.

Acceptance

• The pinned-agents record's claim matches git grep -L '^effort:' output, and the record's as-of date is current.