docs: add inline JS exception to guidelines

Inline JS function calls in HTML attributes (e.g., onclick="myFunction()")
are acceptable for simple interactions

PROJECT_GUIDELINES.md

@@ -28,6 +28,7 @@
 - ❌ **NEVER use custom CSS** - TailwindCSS classes only
   - **⚠️ EXCEPTION**: `templates/error.templ` may have inline CSS because error pages must work when main app fails (404, server errors, CSS fails to load)
 - ❌ **NEVER use JavaScript** - convert all to TypeScript
+  - **⚠️ EXCEPTION**: Inline JS function calls in HTML attributes (e.g., `onclick="myFunction()"`) are acceptable for simple interactions
 - ❌ **NEVER use Object-Oriented Programming** (no classes, inheritance, or this-capture)
 - ✅ **DO use procedural/imperative style** as your default
 - ✅ **DO borrow functional techniques** when they simplify code