Add CI build workflow and badge

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: mathiasconradt

.github/workflows/build.yml

@@ -0,0 +1,13 @@
+name: Build
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Build
+        run: make

README.md

@@ -1,6 +1,6 @@
 # Screen Cursor
 
-[![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=mathiasconradt_screencursor&metric=alert_status)](https://sonarcloud.io/summary/new_code?id=mathiasconradt_screencursor)
+[![Build](https://github.com/mathiasconradt/screencursor/actions/workflows/build.yml/badge.svg)](https://github.com/mathiasconradt/screencursor/actions/workflows/build.yml) [![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=mathiasconradt_screencursor&metric=alert_status)](https://sonarcloud.io/summary/new_code?id=mathiasconradt_screencursor)
 
 Native macOS menu bar app that draws a configurable highlight circle around the cursor.