[Tests]: Add end-to-end CLI smoke test (baseline -> compare) using examples/

## Summary
Add a minimal end-to-end smoke test to validate the core CLI workflow: trace -> export JSON baseline -> export current -> compare.

## Problem
There is no integration test that exercises the full CLI pipeline, so real workflows can break without being caught.

## Proposed Solution
After `examples/` exists (see #40), add a smoke test that:
1) Generates `baseline.json`
2) Generates `current.json`
3) Runs `--compare baseline.json` and asserts exit code + no crash + output files exist

Use `tmp_path` and `subprocess.run`.

## Acceptance Criteria
- Smoke test runs in CI quickly
- Validates exit codes and output files
- Uses `examples/` scripts as fixtures

## Depends On
- #40 (examples/ directory)

## Affected Files
- `tests/`
- `examples/`