docs(readme): cut release-badge cache TTL to 60s

The shields.io release badge inherits Cloudflare's default 5-minute edge
cache, and GitHub Camo proxies on top of that with another 5-minute TTL
— so a fresh tag (v1.5.0) can sit 10 minutes behind on the rendered
README. Adding `cacheSeconds=60` does two things at once: it creates a
new Camo hash for an immediate fresh fetch, and it pins the future
TTL at 60s so the next tag-push propagates to the badge within a
minute instead of a quarter-hour.

README.md

@@ -10,7 +10,7 @@
 
 <p align="center">
   <a href="LICENSE"><img src="https://img.shields.io/badge/License-AGPL--3.0-blue.svg" alt="License: AGPL-3.0" /></a>
-  <a href="https://github.com/MBombeck/HealthLog/releases"><img src="https://img.shields.io/github/v/release/MBombeck/HealthLog?sort=semver&color=success" alt="Latest release" /></a>
+  <a href="https://github.com/MBombeck/HealthLog/releases"><img src="https://img.shields.io/github/v/release/MBombeck/HealthLog?sort=semver&color=success&cacheSeconds=60" alt="Latest release" /></a>
   <a href="https://testflight.apple.com/join/bucuTBpa"><img src="https://img.shields.io/badge/iOS-TestFlight-007AFF?logo=apple&logoColor=white" alt="iOS app on TestFlight" /></a>
   <img src="https://img.shields.io/badge/Self--Hosted-yes-success" alt="Self-Hosted" />
   <img src="https://img.shields.io/badge/Next.js-16-black?logo=next.js" alt="Next.js 16" />