Refactor dashboard JS to ES modules; fix collector strategy loading and add auto-backfill

- Split inline JS into separate ES module files (indicators/, strategies/, ui/, utils/)
- Fix brain.py strategy registry to use MAStrategy directly instead of missing modules
- Add auto-backfill for detected data gaps in collector monitoring loop
- Fix chart resize on sidebar toggle
- Fix chart scrollToTime -> setVisibleLogicalRange

src/api/dashboard/static/js/utils/helpers.js

@@ -0,0 +1,23 @@
+export function downloadFile(content, filename, mimeType) {
+    const blob = new Blob([content], { type: mimeType });
+    const url = URL.createObjectURL(blob);
+    const link = document.createElement('a');
+    link.href = url;
+    link.download = filename;
+    document.body.appendChild(link);
+    link.click();
+    document.body.removeChild(link);
+    URL.revokeObjectURL(url);
+}
+
+export function formatDate(date) {
+    return new Date(date).toISOString().slice(0, 16);
+}
+
+export function formatPrice(price, decimals = 2) {
+    return price.toFixed(decimals);
+}
+
+export function formatPercent(value) {
+    return (value >= 0 ? '+' : '') + value.toFixed(2) + '%';
+}