refactor: dissolve composer extracts and consolidate plugin doctrine

[FrkAk]

Summary

Task Reference: [PYZ-379]

Second tranche of the Claude 5 plugin modernization, stacked on #277. Establishes a single source of truth for every kind of doctrine in the claude-code plugin:

• Dissolve skills/composer/references/ (4 phase-rule extracts + sources.json hash-pin machinery). Phase-unique rules moved into the owning agent body; content mirroring the canonical skills/piyaz/references/ files replaced with pointers. The stale mirror blockquotes in the canonical files are removed.
• Fold composer-planner into composer-researcher: the researcher owns the plan rubric and the draft -> planned transition under its merged mandate, and serves direct "plan " dispatch. agents/composer-planner.md deleted.
• agents/manage.md drops workflows C-F (plan, record completion, resume, propagate); they are owned by the piyaz skill's workflow index and lifecycle.md.
• Convert all 7 DOT digraphs to numbered lists.
• Collapse per-agent status-transition blocks to 1-2 lines; lifecycle.md is the sole state machine. The never-self-promote-to-done rule stays explicit in each dispatched agent body.
• Refine the piyaz skill description (completion and shipping triggers, completion-protocol read-first) and the Hard rules done clause: done is reachable only from in_review, user-reported completion records and sets in_review, unverified or failing criteria hold the task.
• scripts/check-plugins.ts: remove the extract hash-pin machinery and the extract sync entry.

Net for the claude-code plugin: -10,301 words (-16.6%), 0 @-includes, 0 digraphs, 5 files deleted.

Behavioral A/B against the tranche 1 plugin (15 scenarios, 51 runs per arm, paired scoring): mean delta +0.079, 95% CI [0.004, 0.177]; completion-protocol and grounded-record scenarios improved, zero illegal status transitions across the arm.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation

Testing

• Tested locally with bun run dev
• Linting passes (bun run lint)
• Typecheck passes (bun run typecheck)
• Workers smoke passes (bun run build:cf && bun run smoke:cf) — required when this PR touches app/api/**, middleware.ts, worker-cf.ts, or a .node.ts / .workers.ts pair

Notes for reviewer

Brand plugin directories (plugins/codex, plugins/cursor, plugins/antigravity) are intentionally not synced; check:plugins reports drift until the pre-merge bun run sync:plugins on the final PR of this stack.

Docs impact

• Skills/agents catalog regenerates via the Docs Sync workflow; no hand-edited pages affected.

Compliance impact

• none