Story: Add a server-side rate-history endpoint for chart panels

Add a real server-side history endpoint (component/schema TBD — likely ores.marketdata or ores.telemetry, wherever tick/rate persistence already lives) that returns a bounded time series of past values for a given series key (e.g. a CRM pair + crm_name, or a feed binding's symbol) over a requested window/resolution. Chart-style UI panels (starting with the CRM cross-rates matrix's "FX Pair Overview" sparkline) currently have no way to show a trend — the CRM matrix panel's sparkline today is built entirely client-side from this one session's own manual/auto reloads, which means it's empty on first open and forgotten on window close.

The CRM cross-rates matrix's reference mockup (a chart panel per selected pair) is a shape we'll want to repeat across other trading-related UIs, not a one-off. Building each chart's data source ad hoc (client-side rolling buffer, per panel) doesn't scale and gives a worse experience than a proper endpoint would.

• A server-side history endpoint exists, returning a bounded time series of past values for a given series key over a requested window/resolution.
• The CRM cross-rates matrix's sparkline widget consumes the endpoint instead of its client-side-only rolling buffer, so history is available on first open, not just accumulated during the current session.
• The endpoint is reusable by other chart-style UI panels, not bespoke to the CRM matrix.

• projects/ores.qt/marketdata/src/CrmCrossRatesMatrixMdiWindow.cpp (CrmRateSparklineWidget, the current client-side-only rolling buffer this story replaces).

• Market Data Architecture — the producer/authority/consumer remap pattern relevant to where this endpoint should live.