ci: Limit workflow triggers to source files only

Configure build-release.yml to only run on:
- Java source file changes (**.java)
- Workflow file changes

This prevents unnecessary builds when updating documentation
files like README.md or other non-source files.

Author: claude

.github/workflows/build-release.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - main
+    paths:
+      - '**.java'
+      - '.github/workflows/build-release.yml'
   workflow_dispatch:
     inputs:
       version: