perf(release): optimize sandbox creation with tar pipe

Replace cp + rm with tar pipe for sandbox directory copying.
This provides significant performance improvements by:
- Excluding directories during copy (not after)
- Using tar's optimized bulk operations
- Eliminating separate rm -rf cleanup

Performance impact:
- Sandbox tests: 50s+ → 2.45s (~20x faster)
- Full parallel suite: 31.71s → 26.56s (16% faster)
- Overall from baseline: 42.94s → 26.56s (38% faster)

Excluded directories: .git, .release-state, node_modules, .tasks, tmp

Author: Chemaclass

release.sh

@@ -375,9 +375,14 @@ function release::sandbox::create() {
   release::log_info "Creating sandbox at: $SANDBOX_DIR"
 
   # Copy repo content excluding .git, .release-state, node_modules
-  # Using cp + rm for portability (rsync not available on all systems)
-  cp -r . "$SANDBOX_DIR/"
-  rm -rf "$SANDBOX_DIR/.git" "$SANDBOX_DIR/.release-state" "$SANDBOX_DIR/node_modules"
+  # Use tar pipe for faster copying and built-in exclusions
+  tar --exclude='.git' \
+      --exclude='.release-state' \
+      --exclude='node_modules' \
+      --exclude='.tasks' \
+      --exclude='tmp' \
+      -cf - . | tar -xf - -C "$SANDBOX_DIR"
+
   release::log_verbose "Copied project files to sandbox"
 }