feat: add --json/--out flags to lappa path resample + CLI smoke tests (Fixes #52)

[laurentketterle-hub]

Summary

Implements the CLI lappa path resample --step-m fixture rewrite for bounty #52.

Changes

CLI additions (packages/server/src/lappa/cli.py)

• --json flag on path stats: emits a single JSON object with points, path_length_m, net_displacement_m to stdout
• --json flag on path resample: same machine-readable output, plus step_m, original_points, original_length_m
• --out / -o flag on path resample: writes resampled points as a valid JSON fixture with name, points, path_length_m, step_m; creates parent directories automatically
• When both --json and --out are used, the JSON output includes the out key with the resolved path

Tests (packages/server/tests/test_resample_cli_fixture_rewrite.py)

43 new CLI smoke tests:

• 3 stats --json tests (line, square loop, hexagon fixtures)
• 6 resample --json tests (default step, 0.5m, 1.0m, diamond, L-shape, large step)
• 5 resample --out tests (file validity, round-trip, combined --json, custom step, parent dir creation)
• 1 fixture naming test
• 28 parametrized tests (14 fixtures x 2: parseable via --json and writable via --out)

Evidence

$ lappa path stats --file tests/fixtures/sample_path_square_loop.json --json
{"points": 5, "path_length_m": 20.0, "net_displacement_m": 0.0}

$ lappa path resample --file tests/fixtures/sample_path_line.json --step-m 0.5 --json
{"points": 9, "path_length_m": 4.0, "net_displacement_m": 4.0, "step_m": 0.5, "original_points": 3, "original_length_m": 4.0}

$ python -m pytest tests/test_resample_cli_fixture_rewrite.py tests/test_resample.py tests/test_path_stats_cli.py -v
============================= 53 passed in 2.64s ==============================

Closes #52

[laurentketterle-hub]

/attempt 52

[laurentketterle-hub]

Friendly ping 👋 — this PR has been open for 3 days. Is there anything needed for review? Thanks!

[laurentketterle-hub]

/claim