fix: update Node.js runtime from 20 to 24

GitHub Actions is deprecating Node.js 20 runners starting June 2, 2026.
Update action runtime and CI workflows to Node.js 24.

Closes #207

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

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        node-version: [20.x]
+        node-version: [24.x]
 
     steps:
       - name: Checkout

.github/workflows/release.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest ]
-        node-version: [ 20.x ]
+        node-version: [ 24.x ]
 
     steps:
       - name: Checkout