Settled prose design from #3: a reader returning neutral InstrumentGeometry
(digits, pip_size, tick_size, lot_size, base, quote) from <SYMBOL>.meta.json.
Signed autonomously under /boss on the grounding-check PASS; fork decisions
(base/quote pass-through, unknown-version -> None, serde_json, no caching)
are logged on the reference issue.
refs #3
