Relicense from GPLv3 to Apache-2.0 (#81)

* chore: relicense from GPLv3 to Apache-2.0

The app depends on the Capawesome NFC plugin which uses a custom
license that prohibits publishing its source code. This is
incompatible with GPLv3's source distribution requirements.

Apache-2.0 resolves the conflict while preserving all other freedoms.

* docs: update README with license audit findings

- Clarify Capawesome NFC is optional, app compiles without it
- Redefine Pro features as phone hardware sensor reader features
- Correct payment entity to Wizzo Pty Ltd
- Add privacy policy badge
- Clarify React/TypeScript stack

Author: wizzomafizzo