feat(tests): Improve test failure reporting in Makefile

Major improvements to test output clarity and failure diagnostics:

Output Improvements:
- Clean aligned output showing test file + pass/fail status
- Show test count for passing files: "✓ (11 tests)"
- Clear "✗ FAILED" marker for failures (no verbose noise)
- Suppress passing test details (reduces output by ~95%)

Failure Summary:
- Clear visual separator box for failures
- List all failed files with bullet points
- Show specific failed test names with line numbers
- Provide copy-paste commands to re-run failures

Technical Changes:
- Capture test output and only display on failure
- Extract test count from ERT output for passing tests
- Save failure details to temp files for summary
- Apply same improvements to both unit and integration tests

Benefits:
- Instantly see which tests failed (no scrolling)
- Know exactly which test names failed
- Get line numbers for debugging
- Copy-paste commands to re-run specific failures
- Dramatically reduced output verbosity

Example summary:
  Failed test files:
    • test-mousetrap-mode--get-profile-for-mode.el
      Errors:
        FAILED test-foo (line 15)

  Run individual failing tests with:
    make test-file FILE=test-mousetrap-mode--get-profile-for-mode.el

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

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