fix(PR-5020): address post-merge worktree hygiene review

[AceHack]

Summary

• remove the not-yet-main-visible B-0751 row from B-0750 frontmatter graph links while keeping PR backlog(B-0751): per-agent isolated clones architecture — primary checkout is SHARED VIEW + FOR HUMAN; agents NEVER touch it #5019 as prose substrate
• make the current-state worktree hygiene rule use role-reference prose for the empirical quote
• align the main-branch detector comment with its OK-on-success command output

Checks

• git diff --check HEAD~1..HEAD
• bun tools/backlog/generate-index.ts --check
• bun x markdownlint-cli2 .claude/rules/agent-worktree-hygiene-never-hold-main-never-step-on-operator-cleanup-on-pr-merge.md docs/backlog/P2/B-0750-agent-worktree-hygiene-rule-landing-plus-mechanization-target-cleanup-tooling-plus-worktree-pool-primitive-aaron-2026-05-25.md docs/BACKLOG.md
• rg '^<<<<<<<|^=======|^>>>>>>>' .claude/rules/agent-worktree-hygiene-never-hold-main-never-step-on-operator-cleanup-on-pr-merge.md docs/backlog/P2/B-0750-agent-worktree-hygiene-rule-landing-plus-mechanization-target-cleanup-tooling-plus-worktree-pool-primitive-aaron-2026-05-25.md docs/BACKLOG.md

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[Copilot]

Pull request overview

This PR tightens post-merge worktree hygiene documentation by keeping B-0750’s graph links limited to main-visible backlog rows while preserving PR #5019 as prose context.

Changes:

• Removes B-0751 from B-0750 frontmatter composes_with while retaining PR #5019 references in prose.
• Updates the generated backlog index title to match the B-0750 row title.
• Aligns the worktree hygiene rule’s detector comments and empirical-anchor prose with current-state role-reference wording.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
docs/backlog/P2/B-0750-agent-worktree-hygiene-rule-landing-plus-mechanization-target-cleanup-tooling-plus-worktree-pool-primitive-aaron-2026-05-25.md	Updates B-0750 graph/prose references around PR #5019 and B-0751 visibility.
docs/BACKLOG.md	Regenerates the B-0750 index entry from the updated row title.
.claude/rules/agent-worktree-hygiene-never-hold-main-never-step-on-operator-cleanup-on-pr-merge.md	Clarifies expected command output and replaces direct quote with role-reference current-state prose.