fix: show current month data and add caching (#2573)

### Summary

- Add Cache-Control headers to all route responses (1h s-maxage, 2h
stale-while-revalidate)
- Append current month to chart data so graphs stay up-to-date
(cumulative carries forward, else zero)
- Remove `.limit(12)` from growth queries for full history
- Pass isCumulative flag through addZeroMonth
- Deduplicate TransformedData type, remove transformRepoStats

apps/openpage-api/lib/transform-data.ts

@@ -1,6 +1,6 @@
 import { DateTime } from 'luxon';
 
-import { addZeroMonth } from './add-zero-month';
+import { type TransformedData, addZeroMonth } from './add-zero-month';
 
 type MetricKeys = {
   stars: number;
@@ -14,14 +14,6 @@ type DataEntry = {
   [key: string]: MetricKeys;
 };
 
-type TransformData = {
-  labels: string[];
-  datasets: {
-    label: string;
-    data: number[];
-  }[];
-};
-
 type MetricKey = keyof MetricKeys;
 
 const FRIENDLY_METRIC_NAMES: { [key in MetricKey]: string } = {
@@ -38,7 +30,7 @@ export function transformData({
 }: {
   data: DataEntry;
   metric: MetricKey;
-}): TransformData {
+}): TransformedData {
   try {
     if (!data || Object.keys(data).length === 0) {
       return {
@@ -103,7 +95,7 @@ export function transformData({
       ],
     };
 
-    return addZeroMonth(transformedData);
+    return addZeroMonth(transformedData, true);
   } catch (error) {
     return {
       labels: [],
@@ -111,6 +103,3 @@ export function transformData({
     };
   }
 }
-
-// To be on the safer side
-export const transformRepoStats = transformData;