Add HttpFetcher and FileFixtureFetcher with shared _parse_aircraft helper,
DUMP1090_URL constant, realistic fixture data, and full test coverage for
all acceptance criteria (AC1–AC5).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Creates the complete src/planemapper/ layout with all module stubs,
provisioning and renderer subpackages, airports.csv data bundle,
systemd unit files, and full test scaffold. All three quality gates
pass: pytest 12/12, ruff check zero violations, ruff format clean.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Matt Edholm