DAG Mode Step Addition Fixes
Fixed several constraints from the old linear pipeline that broke in DAG mode.
- Terminal steps no longer block adding more steps — adding a text/video/3D output step (alt text, product description, video generation) no longer prevents adding further steps. In DAG mode, new branches are always allowed.
- Port type compatibility enforced on all insertion paths — the "+" button, context menu "Add step after", edge insert, and toolbar "Add Step" all now check port types before auto-connecting. Text output won't connect to image input; incompatible steps are added disconnected instead.
- Toolbar "Add Step" creates disconnected nodes in DAG mode — instead of auto-chaining to the last step (which may be incompatible), new steps appear below with no connections for manual wiring.
- Additional sources default to Library tab instead of Upload
- Context menu "Add source" places the node at click position using screen-to-flow coordinate conversion
- Source node tab styling fixed — Library/Upload/Generate tabs on additional sources now show proper active/hover states (was broken by Tailwind dynamic class purging)
- Node positions persist across sessions — dragged node positions are saved to localStorage and restored on reload