Revert dropdown to simpler positioning approach

Simplified dropdown positioning to fix layering issues:
- Reverted to absolute positioning with inline z-index styles
- Added explicit z-index to dropdown container in streams page
- Removed complex fixed positioning logic that was causing problems

This should resolve dropdown visibility issues while maintaining proper positioning.

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

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

app/streams/page.tsx

@@ -235,7 +235,7 @@ export default function AddStream() {
               Team
             </label>
             <div className="form-row">
-              <div style={{ flex: 1 }}>
+              <div style={{ flex: 1, position: 'relative', zIndex: 10000 }}>
                 <Dropdown
                   options={teams}
                   activeId={formData.team_id}