refactor: remove mock trading functionality from backend and frontend

Removes all mock price simulation features:
- Delete MockPriceManager from backend/data/
- Remove mock_mode, enable_mock, is_mock_mode flags from services
- Remove mock CLI options and config
- Remove mock mode UI components and state from frontend
- Update tests to remove mock references

Now system supports only live and backtest modes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/App.jsx

@@ -291,7 +291,6 @@ export default function LiveTradingApp() {
     financial_datasets: 'FINANCIAL DATASETS',
     local_csv: 'CSV',
     polygon: 'POLYGON',
-    mock: 'MOCK',
     backtest: 'BACKTEST',
   }), []);
 
@@ -415,7 +414,6 @@ export default function LiveTradingApp() {
         pollIntervalDraft={runtimeControls.pollIntervalDraft}
         startDateDraft={runtimeControls.startDateDraft}
         endDateDraft={runtimeControls.endDateDraft}
-        enableMockDraft={runtimeControls.enableMockDraft}
         watchlistDraftSymbols={runtimeControls.watchlistDraftSymbols}
         watchlistInputValue={runtimeControls.watchlistInputValue}
         watchlistSuggestions={runtimeControls.watchlistSuggestions}
@@ -432,7 +430,6 @@ export default function LiveTradingApp() {
         onPollIntervalChange={runtimeControls.setPollIntervalDraft}
         onStartDateChange={runtimeControls.setStartDateDraft}
         onEndDateChange={runtimeControls.setEndDateDraft}
-        onEnableMockChange={runtimeControls.setEnableMockDraft}
         onWatchlistInputChange={runtimeControls.handleWatchlistInputChange}
         onWatchlistInputKeyDown={runtimeControls.handleWatchlistInputKeyDown}
         onWatchlistAdd={runtimeControls.handleWatchlistAdd}