fix: show most recent dates first in return rate and retention tables

- Reverse new player return rate table (most recent day at top)
- Reverse 7- and 30-day retention tables (most recent cohort at top)
- Rename "Day Rate" column to "Return Rate"
- Clarify "Last 14 Days" heading to "Last 14 Days — Completions"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/global/+page.server.ts

@@ -298,8 +298,7 @@ export const load: PageServerLoad = async () => {
 				cohortSize: cohort.size
 			});
 		}
-		series.reverse(); // chronological (oldest first)
-		return series;
+		return series; // newest first (loop iterates i from smallest = most recent)
 	}
 
 	const retention7dSeries = retentionSeries(7, 30);
@@ -331,7 +330,7 @@ export const load: PageServerLoad = async () => {
 		retention7dSeries,
 		retention30dSeries,
 		overallReturnRate,
-		newPlayerReturnSeries: newPlayerReturnSeries.slice(-30),
+		newPlayerReturnSeries: newPlayerReturnSeries.slice(-30).reverse(),
 		newPlayerReturnVelocity: {
 			current7dAvg: current7dReturnAvg,
 			prior7dAvg: prior7dReturnAvg,