fix: surface empty OHLCV fetch as a warning, not success

Fetching a symbol the provider doesn't cover (e.g. RHM/Rheinmetall — Alpaca
serves US listings only) returned 0 bars but reported "complete · Successfully
ingested 0 records", which the UI showed as green success.

fetch_and_ingest now returns a distinct `no_data` status when the provider
returns nothing AND the ticker has no history (vs. "already up to date" when bars
exist). The fetch endpoint maps it to a `warning` source status, and the fetch
toast renders it as ⚠ with the provider message instead of success.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/api/ingestion.ts

@@ -1,7 +1,7 @@
 import apiClient from './client';
 
 export interface IngestionSourceResult {
-  status: 'ok' | 'error' | 'skipped';
+  status: 'ok' | 'error' | 'skipped' | 'warning';
   message?: string | null;
   records?: number;
   classification?: string;

frontend/src/lib/ingestionStatus.ts

@@ -25,6 +25,9 @@ export function summarizeIngestionResult(
     if (info.status === 'ok') {
       return `${label} ✓`;
     }
+    if (info.status === 'warning') {
+      return `${label} ⚠${info.message ? `: ${info.message}` : ': no data'}`;
+    }
     if (info.status === 'skipped') {
       return `${label}: skipped${info.message ? ` (${info.message})` : ''}`;
     }
@@ -32,8 +35,10 @@ export function summarizeIngestionResult(
   });
 
   const hasError = entries.some(([, source]) => source.status === 'error');
+  const hasWarning = entries.some(([, source]) => source.status === 'warning');
   const hasSkip = entries.some(([, source]) => source.status === 'skipped');
-  const toastType: IngestionToastType = hasError ? 'error' : hasSkip ? 'info' : 'success';
+  // A warning (e.g. 0 bars returned) must not read as success.
+  const toastType: IngestionToastType = hasError ? 'error' : hasWarning || hasSkip ? 'info' : 'success';
 
   return {
     toastType,