Task: Build knowledge documents for currency pairs

Take Marco's freeform notes on currency pairs and turn them into properly-fitted ORE Studio knowledge documents: broken up into small, self-contained zettelkasten units (not one monolith), each tagged and indexed per the doc-add-knowledge convention, and cross-linked via org-roam [[id:...]] links — both amongst themselves and to existing related documents (e.g. the cross rates matrix). Produce an index document that ties the set together.

• [X] Marco's notes are decomposed into multiple small, self-contained knowledge documents (one topic per document), scaffolded via compass add knowledge.
• [X] Each document is tagged appropriately and linked from an index document.
• [X] Documents are cross-linked to each other and to existing related documents (e.g. the cross rates matrix) via org-roam [[id:...]] links, not plain text references.
• [X] compass index is re-run so the new documents are searchable.

Read the source notes (~/Development/Notebooks/summaries/currency-pairs.org) and cross-checked them against the existing CRM knowledge cluster in doc/knowledge/domain/ before writing anything, to avoid duplicating fx_currency_conventions.org and fx_spot_date_and_settlement.org, which already covered base/quote precedence, G11/EM, and spot days.

Split the remaining, not-yet-covered material into five new zettels plus a hub note, all scaffolded via compass add knowledge: fx_deliverability_and_ndf, fx_pip_tick_and_pip_factor, fx_pair_classification, fx_currency_pair_entity_fields, fx_valuation_spot_date_and_overnight, and the fx_currency_pairs hub. Extended the two overlapping docs instead of duplicating them (fixing sources/barrier inversion into conventions; business-day vs settlement-day and holiday calendars into spot/settlement).

Renamed the non-idiomatic "mfactor" to the desk-standard pip factor throughout, including in an older doc (fx_spot_rate_derivation_mechanics.org) that used the same term.

After the docs were in place, reorganised doc/knowledge/knowledge.org on request: split the flat * Domain list into topic subheadings (FX and market data conventions, Rates and curves, Risk/valuation/reporting, Trading and front office, Data quality, Synthetic data generation), moved infrastructure/PoC-flavoured docs (marketdata inventory, FX spot PoC, generator library, NATS polymorphic types) into * Architecture where they belong, and removed the nested child-bullet lists under the CRM and Currency pairs hub entries (redundant with the hub pages' own concept maps).

Verified via compass show (id-link resolution) and a full compass build --direct site (catches any broken id-link).

Shipped six new knowledge documents under doc/knowledge/domain/ (fx_currency_pairs hub, fx_deliverability_and_ndf, fx_pip_tick_and_pip_factor, fx_pair_classification, fx_currency_pair_entity_fields, fx_valuation_spot_date_and_overnight), extended fx_currency_conventions.org and fx_spot_date_and_settlement.org with the notes' non-duplicate material, and fixed "mfactor" → "pip factor" wherever it appeared. Reorganised the knowledge.org Domain index into topic subheadings and relocated infrastructure/PoC docs into Architecture. compass index and a full site build both ran clean — no broken id-links. Committed as 222f448aa on feature/currency-pair-refdata.