feat: Agent-friendly output improvements

[witqq]

Summary

Based on production usage in MCP Moira project, several improvements would make testfold more agent-friendly:

1. Clear Agent Instructions on Failure

When tests fail, output explicit instructions for AI agents:

┌─────────────────────────────────────────────────────────────┐
│  AGENT INSTRUCTIONS:                                        │
│                                                             │
│  1. Read .md files above - they contain full error info    │
│  2. DO NOT re-run tests - artifacts will be overwritten    │
│  3. DO NOT read .log files - use .md reports instead       │
│  4. Fix issues based on failure reports, then re-run tests │
└─────────────────────────────────────────────────────────────┘

Why: Agents often waste tokens re-running tests or reading full logs when failure reports already exist.

2. List Exact Failure Report Paths

Instead of just showing the failures directory, list each .md file:

Unit (2 failed):
  📄 test-results/failures/unit/01-auth-login-should-validate-token.md
  📄 test-results/failures/unit/02-user-service-should-create-user.md

Why: Agent can immediately read specific files without listing directory.

3. Test File Filter with Auto-Skip

When running with a test file argument, suites that don't match should show "Skipped" not "Failed":

testfold -- auth.test.ts

Output:

⊘ Integration Tests Skipped (no matching files)
⊘ E2E Tests Skipped (no matching files)
✓ Unit Tests: 15 passed (2.1s)

Current behavior: "No tests found" is treated as failure.

4. Glob-Based Test File Resolution

Allow passing just filename and resolve it recursively:

testfold -- user-service.test.ts
# Resolves to: tests/unit/services/user-service.test.ts

Show resolution in output:

🔍 Resolved test file to: tests/unit/services/user-service.test.ts

Why: Agents don't always know full path structure.

5. Failure Marker in Artifacts Table

Mark failed suites clearly in artifacts summary:

📂 All artifacts: test-results/
Unit       unit.json | unit.log | failures/unit/ ◀ READ THIS
E2E        e2e.json | e2e.log | failures/e2e/

Implementation Notes

These changes are already implemented and tested in MCP Moira's test runner (tests/run-all-tests.js). Can provide reference implementation.