docs/chore: audit OpenGD77/1701 import-export implementation against reference docs

[pskillen]

Problem

The import/export documentation was collated and restructured under docs/features/import-export/ (#84), and the authoritative wire-format reference lives under docs/reference/opengd77/ (#43).

The docs describe the intended behaviour, but the shipped OpenGD77/Baofeng 1701 import and export code has not been systematically audited against them since the restructure. Where docs and code disagree, code wins until fixed (per the reference hub) — but we should confirm they actually agree, and ticket any gaps.

This item is carried as open debt in docs/features/import-export/outstanding.md.

Intended outcome

A documentation/accuracy audit (not a feature). Walk every documented behaviour against the implementation and either confirm alignment or file follow-up issues for code/doc gaps.

Scope — confirm code matches docs

• Per-column mapping — every column in docs/reference/opengd77/ (channels, zones, contacts, tg-lists, dtmf-aprs) matches src/lib/import/opengd77/parse.ts + columns.ts and src/lib/export/opengd77/serialise.ts.
• Conversion rules — booleans (Yes/No), VOX (Off/On), ID Type → TalkGroup/Contact, name-based FK denormalisation.
• Classification — detectKind heuristics in opengd77/README.md match adapter.ts.
• Skip vs error — DTMF.csv/APRS.csv skipped on import; header-only on export; parse-failure vs skip behaviour.
• Cardinality — 1701 profile constants (80 zone members, 32 TG list members) match hard-coded export padding/truncation.
• Lossy fields — vendorExtras round-trip, app-only fields (hideFromMap), header-only files behave as documented.
• Merge semantics — match keys, idempotent re-import, zone member re-resolution match hub README and importMerge.ts.

Method

1. Read each reference/adapter doc; tick or flag each documented behaviour against code.
2. Cross-check existing tests (parse.test.ts, roundtrip.test.ts, importMerge.test.ts, system suite) cover the documented behaviour; note coverage gaps.
3. For each discrepancy: fix the doc if the code is correct, or file a code-bug follow-up issue (code wins until fixed).
4. Tick the audit item in outstanding.md when complete.

Affected

• docs/reference/opengd77/*.md, docs/features/import-export/**
• src/lib/import/opengd77/, src/lib/export/opengd77/
• Possibly new follow-up issues for code gaps

Out of scope

• Implementing the radio profile picker (#72).
• Modelling APRS/DTMF (tracked in outstanding.md).
• New vendor formats.

Notes

• Follow-up to #84; discovered-debt item in outstanding.md.
• Docs-only unless the audit surfaces code bugs worth ticketing separately.

[pskillen]

Tracked under epic #93 (pristine vendor-neutral internal data model). This is Phase 0 of that epic.