Get last-known prices for equity/forex/commodity symbols

Returns last-known prices for a fixed allow-list of stock, ETF, forex, and commodity symbols (e.g. AAPL, SPY, EURUSD, XAUUSD), mapped internally to their upstream tickers. A request is served straight from cache only if every requested symbol is already cached. Otherwise, missing symbols are fetched and merged into the existing cache, and only the newly-fetched subset is returned with cached: false — symbols already warm in the cache are NOT re-included in that response body (the endpoint returns either the full cached hit set with cached: true, or just the freshly-fetched symbols with cached: false, never a merge of both in one response). Returns prices even when markets are closed (uses the last regular-session print) so the UI is never blank outside trading hours. Auth differs from every other endpoint in this router: this accepts a first-party session JWT (Authorization: Bearer ...) or an internal admin credential — it does not accept the X-Client-Id/X-Api-Key/ X-Api-Secret API-key headers that the rest of /markets/* accepts.