chore: Update .gitignore for build artifacts

Adds patterns to ignore build-tmp/, *.log, and *.key files
which are generated during the build process and should not be
committed to version control.

💘 Generated with Crush

Assisted-by: Gemini 2.5 Flash via Crush <crush@charm.land>

.gitignore

@@ -35,3 +35,12 @@ Thumbs.db
 *.deb
 *.tar.gz
 *.tar.xz
+
+# Build temporary directory
+build-tmp/
+
+# Log files
+*.log
+
+# Test keys (WireGuard)
+*.key