perf: add CDN Cache-Control headers to streak API route (JhaSourav07#267)

## Description
Fixes JhaSourav07#69

Added CDN Cache-Control headers to the streak API route:
- Replaced dynamic s-maxage with fixed `s-maxage=14400` (4 hours)
- Added `stale-while-revalidate=86400` (24 hours)
- Updated error responses (500) to use `public, s-maxage=60`

## Pillar
🛠️ Other (Bug fix, refactoring, docs)

## Checklist
- [x] I have read the CONTRIBUTING.md file.
- [x] My commits follow the Conventional Commits format.
- [x] I have made sure that I have only one commit to merge in this PR.

Author: HarshParmar029

app/api/streak/route.test.ts

@@ -344,7 +344,7 @@ describe('GET /api/streak', () => {
 
       const response = await GET(makeRequest({ user: 'octocat' }));
 
-      expect(response.headers.get('Cache-Control')).toBe('no-cache');
+      expect(response.headers.get('Cache-Control')).toBe('public, s-maxage=60');
     });
 
     it('returns a valid 500 SVG even when something non-Error is thrown', async () => {

app/api/streak/route.ts

@@ -11,7 +11,6 @@ import { streakParamsSchema } from '../../../lib/validations';
 export async function GET(request: Request) {
   const { searchParams } = new URL(request.url);
 
-  // Parse and validate all incoming params through Zod schema
   const parseResult = streakParamsSchema.safeParse(Object.fromEntries(searchParams.entries()));
   try {
     if (!parseResult.success) {
@@ -47,8 +46,6 @@ export async function GET(request: Request) {
     const from = year ? `${year}-01-01T00:00:00Z` : undefined;
     const to = year ? `${year}-12-31T23:59:59Z` : undefined;
 
-    // Validate the IANA timezone name early so callers get a clear 400 rather than a
-    // silent fallback or a 500. Intl.DateTimeFormat throws a RangeError on unknown zones.
     const tzParam = searchParams.get('tz');
     let timezone = 'UTC';
     if (tzParam) {
@@ -59,27 +56,24 @@ export async function GET(request: Request) {
         return new NextResponse(`Invalid "tz" parameter: "${tzParam}"`, { status: 400 });
       }
     }
+
     const isAutoTheme = themeName === 'auto';
     const isRandomTheme = themeName === 'random';
     const selectedTheme = (() => {
       if (isAutoTheme) return themes.light;
-
       if (isRandomTheme) {
         const keys = Object.keys(themes);
         const randomKey = keys[Math.floor(Math.random() * keys.length)];
         return themes[randomKey] || themes.dark;
       }
-
       return themes[theme] || themes.dark;
     })();
 
     const params: BadgeParams = {
       user,
-
       bg: isAutoTheme ? selectedTheme.bg : bg || selectedTheme.bg,
       text: isAutoTheme ? selectedTheme.text : text || selectedTheme.text,
       accent: isAutoTheme ? selectedTheme.accent : accent || selectedTheme.accent,
-
       radius,
       speed,
       scale,
@@ -100,9 +94,6 @@ export async function GET(request: Request) {
     const stats = calculateStreak(calendar, timezone);
     const svg = generateSVG(stats, params, calendar);
 
-    // 4. Calculate Cache Control — reset at local midnight when ?tz= is supplied,
-    //    otherwise fall back to UTC midnight (original behaviour).
-    //    Random themes are never cached because their output changes on every request.
     const secondsToMidnight = tzParam
       ? getSecondsUntilMidnightInTimezone(timezone)
       : getSecondsUntilUTCMidnight();
@@ -140,7 +131,6 @@ export async function GET(request: Request) {
       const match = message.match(/"([^"]+)"|login of '([^']+)'/);
       const badUsername =
         match?.[1] ?? match?.[2] ?? (parseResult.success ? parseResult.data.user : 'unknown');
-
       const svg = generateNotFoundSVG(badUsername, errBg, errAccent, errText, errRadius, errSpeed);
       return new NextResponse(svg, {
         status: 404,
@@ -152,6 +142,7 @@ export async function GET(request: Request) {
         },
       });
     }
+
     const errorSvg = `
       <svg xmlns="http://www.w3.org/2000/svg" width="400" height="150">
         <rect width="100%" height="100%" fill="#2d0000" rx="8"/>
@@ -165,7 +156,7 @@ export async function GET(request: Request) {
       status: 500,
       headers: {
         'Content-Type': 'image/svg+xml',
-        'Cache-Control': 'no-cache',
+        'Cache-Control': 'public, s-maxage=60',
       },
     });
   }