Add aviation coverage matrix (docs/coverage/aviation.md)

[kmadan]

Goal

Add `docs/coverage/aviation.md` mapping every policy under the following directories to its source obligation:

• `industry_specific/aviation/v1/`
• `international/icao/v1/`
• `international/faa/v1/`
• `international/easa/v1/`
• `international/standards/v1/`

Follow the format of docs/coverage/eu-ai-act.md.

Why this matters

Aviation is GOPAL's strongest vertical (17 policies, plus another 9 across ICAO/FAA/EASA/standards). It's also the most opaque to outside contributors — they don't know what's covered because no map exists. A coverage matrix unblocks the next wave of contributions.

What to cite

Each row should cite the source: ICAO Doc 10019 section, RTCA DO-365 / DO-366 paragraph, FAA Part 107 / Remote ID, EASA Regulation 2019/947 article, ASTM F3442, ISO 21384.

Acceptance criteria

• Matrix lists every aviation/safety-critical policy file
• Each row marks Implemented / Scaffold / Planned
• docs/coverage/README.md links to the new matrix
• At least one "📋 Planned" row identifies a real gap that would attract a follow-up PR

Get help

This is mostly a reading task — no Rego required. Aviation regulatory background welcome but not required.