Track safe CLI and API errors

[wydrox]

Summary

• add privacy-safe cli_error and api_error analytics events
• route CLI console script through main_entry so non-zero exits are tracked
• add API middleware to track 4xx/5xx responses and unhandled endpoint exceptions
• allow only safe string fields (command, endpoint, error_type, error_stage) plus numeric codes; no stack traces, prompts, request bodies, model names, repo IDs, or paths
• bump package version to 0.5.3

Validation

• uv run ruff check .
• PPMLX_ANALYTICS_ENABLED=0 uv run pytest -q (231 passed)
• uv build
• uvx --from dist/ppmlx-0.5.3-py3-none-any.whl ppmlx --version -> ppmlx 0.5.3

Notes

• MLX dependency constraints are intentionally unchanged from main.