Add stream deletion functionality and improve UI

- Add delete button to each stream with confirmation modal
- Implement DELETE endpoint that removes sources from OBS before database deletion
- Fix dropdown positioning issue when scrolling by removing scroll offsets
- Change add stream form to use Twitch username instead of full URL
- Automatically calculate Twitch URL from username (https://twitch.tv/{username})
- Add username validation (4-25 chars, alphanumeric and underscores only)
- Improve "View Stream" link visibility with button styling
- Ensure streams list refreshes immediately after deletion

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

components/Dropdown.tsx

@@ -49,13 +49,27 @@ export default function Dropdown({
   }, [controlledIsOpen, isOpen, onToggle]);
 
   useEffect(() => {
-    if ((controlledIsOpen ?? isOpen) && buttonRef.current && mounted) {
-      const rect = buttonRef.current.getBoundingClientRect();
-      setDropdownPosition({
-        top: rect.bottom + window.scrollY + 4,
-        left: rect.left + window.scrollX,
-        width: rect.width
-      });
+    const updatePosition = () => {
+      if ((controlledIsOpen ?? isOpen) && buttonRef.current && mounted) {
+        const rect = buttonRef.current.getBoundingClientRect();
+        setDropdownPosition({
+          top: rect.bottom + 4,
+          left: rect.left,
+          width: rect.width
+        });
+      }
+    };
+
+    updatePosition();
+
+    if ((controlledIsOpen ?? isOpen) && mounted) {
+      window.addEventListener('scroll', updatePosition, true);
+      window.addEventListener('resize', updatePosition);
+      
+      return () => {
+        window.removeEventListener('scroll', updatePosition, true);
+        window.removeEventListener('resize', updatePosition);
+      };
     }
   }, [controlledIsOpen, isOpen, mounted]);