Add a headless smoke-test harness for the Presto microPython app using
pimoroni-emulator mock modules. A PRESTO_TEST_MODE=1 guard prevents
main() from running at import time so draw functions can be called
directly from tests.
- presto/main.py: wrap main() with PRESTO_TEST_MODE guard
- presto/tests/: conftest with emulator fixtures, 7 smoke tests
- presto/mise.toml: add [tasks.test]
- presto/README.md, presto/AGENTS.md: add Testing section
- .gitignore: exclude test __pycache__, pytest_cache, fixture pngs
Claudio Ortolina