Add a raw-data viewer to Review Queue cards, improve chart color palette

A "Raw data" button at the bottom right of each card opens a modal with the
full activity/laps/assignment JSON (embedded RawJSON strings parsed back
into objects for readability), to make it easier to inspect exactly what
data is available when iterating on the charts.

Phase band colors (warm-up/effort/recovery/cool-down) previously reused the
same blue/red as the pace/HR accent colors, making them hard to tell apart.
New palette (amber/pink/teal/violet) avoids both accents entirely.

frontend/src/App.css

@@ -262,6 +262,57 @@ button:disabled {
   display: inline-block;
 }
 
+.review-item-footer {
+  display: flex;
+  justify-content: flex-end;
+  margin-top: 0.5rem;
+}
+
+.raw-data-button {
+  font-size: 0.75rem;
+  padding: 0.25rem 0.6rem;
+  color: #9aa0ab;
+}
+
+.modal-backdrop {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.6);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 100;
+}
+
+.modal-content {
+  background: #14161c;
+  border: 1px solid #2a2d35;
+  border-radius: 8px;
+  width: min(720px, 90vw);
+  max-height: 80vh;
+  display: flex;
+  flex-direction: column;
+}
+
+.modal-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 0.75rem 1rem;
+  border-bottom: 1px solid #2a2d35;
+  font-weight: 600;
+}
+
+.modal-json {
+  margin: 0;
+  padding: 1rem;
+  overflow: auto;
+  font-size: 0.8rem;
+  line-height: 1.4;
+  white-space: pre-wrap;
+  word-break: break-word;
+}
+
 .kinds-table {
   width: 100%;
   border-collapse: collapse;