Story: Rate display conventions: convention-aware formatting across all Qt rate surfaces (FX + IR)

CrmCrossRatesMatrixMdiWindow already does this right: a prior task replaced its hand-rolled QString::number(rate, 'f', 5) with a stateless, convention-aware crm_rate_formatter (ores.marketdata.client/ presentation) that resolves currency_pair_convention via a cache and snaps/renders at the pair's real pip_factor=/=tick_size=/ =decimal_places. But that fix only reached the CRM matrix's own cells — every other rate-displaying surface in the Qt client still hand-formats with a hardcoded precision, including a residual gap in the same CRM window (its overview-panel sparkline label, missed by the original wiring). Surveyed sites, all currently hardcoded:

• CurveSnapshotMdiWindow — Grid/History tabs, shared by both FX and IR series (dispatched by series_type) — hardcoded \'f\=, 6= everywhere, delta-bp column hardcoded \'f\=, 1=.
• CrmCrossRatesMatrixMdiWindow's overview panel (selected-pair label + sparkline) — hardcoded \'f\=, 5=, missed by the original formatter wiring.
• CurveShapePreviewChart=/=SampleShortRatePathsChart (IR) and SamplePricePathsChart (FX) — QtCharts QValueAxis default label format, no unit/precision awareness at all.
• IrCurveEditor (Simple-mode value label, Advanced table), IrCurveGenerationConfigDetailDialog=/=HistoryDialog, FxSpotGenerationConfigDetailDialog=/=HistoryDialog, MarketSimulatorWindow summary panel — all bare QString::number(double) (%g, 6 significant figures) or a hardcoded \'g\=/\='f\==.

IR has no convention entity to even resolve in the first place: floating_index_type is bare code+description, overnight_index_convention holds fixing calendar/day-count/ settlement-lag but no display precision/unit. This story:

• Closes the residual FX gaps by reusing existing currency_pair_convention data and extending the crm_rate_formatter architecture's pattern (stateless, presentation-layer, convention-in/strings-out, DB/NATS-free) to the non-CRM FX surfaces above — the pip/tick-snapping logic itself stays CRM/FX-spot-specific, not generalised past its own domain.
• Adds an ir_index_convention table mirroring currency_pair_convention's shape (keyed by floating_index_type.code, since the separate, unrelated index-catalog consolidation task hasn't landed yet), plus a sibling ir_rate_formatter following the same architectural contract. Research confirms real trading-system practice does not offer a global percent/bp display toggle: an outright rate level (a fixing, a swap rate, a curve point) is always quoted in percent at a precision fixed by the instrument/currency, never in bp — bp is reserved for a different quantity entirely (deltas, spreads over a benchmark, DV01/risk), not an alternate unit for the same level. CurveSnapshotMdiWindow's existing Δ (bp) column already gets this right by instinct (level in the grid, tick-to-tick move separately in bp) — so ir_index_convention only needs decimal_places, mirroring currency_pair_convention, not a unit- switching mechanism.
• Wires both formatters into every surveyed site. Since every rate level stays in percent, chart axes only need per-index decimal precision on their label format, not a data-rescaling step — no percent/bp axis-unit switching to design around.

Absorbs the remaining scope of the narrower, IR-only "IR rate display/quoting conventions" task in the IR Rates follow-ups story, which is marked ABANDONED with a pointer here rather than tracked twice — the FX and IR gaps are the same architectural problem and are better solved together in one pass than designed independently and reconciled later.

• CurveSnapshotMdiWindow (Grid/History, both FX and IR series) and CrmCrossRatesMatrixMdiWindow's overview panel consume currency_pair_convention=/=ir_index_convention via a formatter instead of a hardcoded \'f\=, N=.
• CurveShapePreviewChart, SampleShortRatePathsChart, SamplePricePathsChart axis labels use per-index/pair decimal precision instead of QtCharts' default format.
• IrCurveEditor, IR/FX config detail and history dialogs, and MarketSimulatorWindow's summary panel use the shared formatter(s) instead of bare QString::number(double).
• A new ir_index_convention table (keyed by floating_index_type.code) with decimal_places, backed by a research note on real per-currency/index-tier precision (G10 overnight RFRs vs EM curves), and a sibling ir_rate_formatter matching crm_rate_formatter's architectural contract (stateless, presentation-layer, DB/NATS-free).
• Real Catch2 coverage of ir_rate_formatter, independent of any Qt/NATS harness, matching crm_rate_formatter_tests.cpp's own coverage shape (precision rounding, missing-convention fallback).

• A user-facing percent/basis-point display toggle — real trading systems don't offer one for outright rate levels (see Goal); bp stays reserved for deltas, which CurveSnapshotMdiWindow already shows correctly.
• Consolidating floating_index_type=/=overnight_index_convention into one index entity — tracked separately by Normalize floating-rate index reference data; ir_index_convention keys off the current floating_index_type.code and can be re-keyed later if that task changes the identifier space.
• Extending crm_rate_formatter's own pip/tick-snapping logic beyond CRM — the non-CRM FX surfaces reuse the architectural pattern, not the CRM-specific formatter itself.