fix: stabilize subgraph promoted widget identity and rendering (#9896)

## Summary

Fix subgraph promoted widget identity/rendering so on-node widgets stay
correct through configure/hydration churn, duplicate names, and
linked+independent coexistence.

## Changes

- **Subgraph promotion reconciliation**: stabilize linked-entry identity
by subgraph slot id, preserve deterministic linked representative
selection, and prune stale alias/fallback entries without dropping
legitimate independent promotions.
- **Promoted view resolution**: bind slot mapping by promoted view
object identity (`getSlotFromWidget` / `getWidgetFromSlot`) to avoid
same-name collisions.
- **On-node widget rendering**: harden `NodeWidgets` identity and dedup
to avoid visual aliasing, prefer visible duplicates over hidden stale
entries, include type/source execution identity, and avoid collapsing
transient unresolved entries.
- **Mapping correctness**: update `useGraphNodeManager` promoted source
mapping to resolve by input target only when the promoted view is
actually bound to that input.
- **Subgraph input uniqueness**: ensure empty-slot promotion creates
unique input names (`seed`, `seed_1`, etc.) for same-name multi-source
promotions.
- **Safety fix**: guard against undefined canvas in slot-link
interaction.
- **Tests/fixtures**: add focused regressions for fixture path
`subgraph_complex_promotion_1`, linked+independent same-name cases,
duplicate-name identity mapping, dedup behavior, and input-name
uniqueness.

## Review Focus

Validate behavior around transient configure/hydration states (`-1` id
to concrete id), duplicate-name promotions, linked representative
recovery, and that dedup never hides legitimate widgets while still
removing true duplicates.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9896-fix-stabilize-subgraph-promoted-widget-identity-and-rendering-3226d73d365081c8a1e8d0a5a22e826d)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>

src/components/rightSidePanel/parameters/SectionWidgets.vue

@@ -23,6 +23,7 @@ import { HideLayoutFieldKey } from '@/types/widgetTypes'
 
 import { GetNodeParentGroupKey } from '../shared'
 import WidgetItem from './WidgetItem.vue'
+import { getStableWidgetRenderKey } from '@/core/graph/subgraph/widgetRenderKey'
 
 const {
   label,
@@ -272,7 +273,7 @@ defineExpose({
         <TransitionGroup name="list-scale">
           <WidgetItem
             v-for="{ widget, node } in widgets"
-            :key="`${node.id}-${widget.name}-${widget.type}`"
+            :key="getStableWidgetRenderKey(widget)"
             :widget="widget"
             :node="node"
             :is-draggable="isDraggable"