fix: clear stale widget slotMetadata on link disconnect (#9885)

## Summary
Fixes text field becoming non-editable when a previously linked input is
removed from a custom node.

## Problem
When a widget's input was promoted to a slot, connected via a link, and
then the input was removed (e.g., by updating the custom node
definition), the widget retained stale `slotMetadata` with `linked:
true`. This prevented the widget from being editable.

## Solution
In `refreshNodeSlots`, removed the `if (slotInfo)` guard so
`widget.slotMetadata` is always assigned — either to valid metadata or
`undefined`. This ensures stale linked state is cleared when inputs no
longer match widgets.

## Acceptance Criteria
1. Text field remains editable after promote→connect→disconnect cycle
2. Text field returns to editable state when noodle disconnected
3. No mode switching needed to restore editability

## Testing
- Added regression test: "clears stale slotMetadata when input no longer
matches widget"
- All existing tests pass (18/18 in affected file)

---
**Note: This PR currently contains only the RED (failing test) commit
for TDD verification. The GREEN (fix) commit will be pushed after CI
confirms the test failure.**

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9885-fix-clear-stale-widget-slotMetadata-on-link-disconnect-3226d73d365081269319c027b42d9f6b)
by [Unito](https://www.unito.io)

src/composables/graph/useGraphNodeManager.ts

@@ -520,8 +520,7 @@ export function useGraphNodeManager(graph: LGraph): GraphNodeManager {
 
     // Update only widgets with new slot metadata, keeping other widget data intact
     for (const widget of currentData.widgets ?? []) {
-      const slotInfo = slotMetadata.get(widget.slotName ?? widget.name)
-      if (slotInfo) widget.slotMetadata = slotInfo
+      widget.slotMetadata = slotMetadata.get(widget.slotName ?? widget.name)
     }
   }