Add synthetic taker flow, timestamps, open interest, and metadata to indicator harness; improve error messages and theme tweaks

- Generate buy/sell volume split with random fractions
- Add nanosecond timestamps for OHLC extremes within 1-minute bars
- Include open interest as separate random walk
- Add num_trades and quote_volume derived fields
- Derive extra_columns dynamically from indicator input requirements instead of hardcoded volume check
- Improve input_series error message clarity
- Adjust ChatPanel background color for user messages

web/src/components/ChatPanel.vue

@@ -601,7 +601,7 @@ const chatStyles = {
   },
   message: {
     background: '#141414',
-    backgroundMe: '#089981',
+    backgroundMe: '#1c1c1c',
     color: '#dbdbdb',
     colorStarted: '#8a8a8a',
     backgroundDeleted: '#0f0f0f',