activity-stats: shared StatRow + canonical metrics across surfaces

Implements the activity-stats change (specs/activity-stats):

- gpx: `movingTime(tracks)` — moving seconds from trackpoint timestamps,
  excluding stationary spans + long gaps; null when no timestamps.
- stats.ts: pure formatters (distance/elevation/duration/speed/pace),
  sport-aware `deriveRate` (pace for foot sports, speed otherwise, speed
  default), and `activityStatItems` encoding the canonical order
  (distance · time · [moving] · pace/speed · ascent · descent; compact subset).
- StatRow: one shared presentational component (size sm/lg), adopted on the
  activity detail (full set; loader derives moving time), route detail
  (distance/ascent/descent), feed card + profile list (compact).
- i18n: journal.stats.* in en + de.

Tests: movingTime (stationary/gap exclusion, moving ≤ elapsed), deriveRate,
formatters, activityStatItems ordering + compact, StatRow render (jsdom).
typecheck + lint + unit (gpx 63, journal 311) green.

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

apps/journal/app/components/StatRow.tsx

@@ -0,0 +1,34 @@
+import type { StatItem } from "~/lib/stats";
+
+/**
+ * The one shared headline-stat presentation. Surfaces pass an ordered list of
+ * {value, label} items (built via `activityStatItems`); the component never
+ * fetches or formats. `size="lg"` is the detail-page treatment; the default
+ * compact size is for feed cards and the profile list.
+ */
+export function StatRow({
+  items,
+  size = "sm",
+  className,
+}: {
+  items: StatItem[];
+  size?: "sm" | "lg";
+  className?: string;
+}) {
+  if (items.length === 0) return null;
+  const valueCls =
+    size === "lg"
+      ? "text-2xl font-bold text-gray-900"
+      : "text-sm font-semibold text-gray-900";
+  const gap = size === "lg" ? "gap-6" : "gap-x-4 gap-y-1";
+  return (
+    <dl className={`flex flex-wrap ${gap}${className ? ` ${className}` : ""}`}>
+      {items.map((it) => (
+        <div key={it.label}>
+          <dd className={valueCls}>{it.value}</dd>
+          <dt className="text-xs text-gray-500">{it.label}</dt>
+        </div>
+      ))}
+    </dl>
+  );
+}