docs(agents): correct coverage floor to 75% (matches .settings.yaml)

[yuanchen8911]

Summary

.claude/CLAUDE.md (and its CI-synced AGENTS.md mirror) stated the test-coverage gate enforces a 70% floor. The enforced value is 75%: make test-coverage reads quality.coverage_threshold: '75' from .settings.yaml via yq (Makefile:19); the 70 at Makefile:21 is only a fallback when that read returns empty.

Fixes the line in both files (line 584) from 70% → 75%.

Type of Change

• Documentation update

Testing

make check-agents-sync   # OK (CLAUDE.md and AGENTS.md mirror in sync)

Doc-only change to the agent-rules files; check-agents-sync confirms the mirror stays consistent.

Checklist

• Changes follow existing patterns
• Commit is signed (-S -s)

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Enterprise

Run ID: cab7fccd-83bb-4806-8967-863a46388404

📥 Commits

Reviewing files that changed from the base of the PR and between 3eb13ff and 8d5406c.

📒 Files selected for processing (2)

• .claude/CLAUDE.md
• AGENTS.md

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📝 Walkthrough

Walkthrough

Two documentation files (AGENTS.md and .claude/CLAUDE.md) each have a single line updated: the project-wide test coverage floor enforced by make test-coverage is changed from 70% to 75%. No code, logic, or other documentation sections are modified.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the docs-only change and the corrected 75% coverage floor.
Description check	✅ Passed	The description matches the changeset and explains the 70% to 75% documentation correction.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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