fix: support progressive fallback for deeply nested model directories

Previously, modelToNode fallback only tried exact match then top-level
segment (e.g., "a/b/c" → "a"), skipping intermediate paths. Now tries
all parent paths progressively ("a/b/c" → "a/b" → "a"), fixing custom
nodes with longer nested directory structures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/stores/modelToNodeStore.ts

@@ -75,8 +75,8 @@ export const useModelToNodeStore = defineStore('modelToNode', () => {
 
   /**
    * Find providers for modelType with hierarchical fallback.
-   * Tries exact match first, then falls back to top-level segment (e.g., "parent/child" → "parent").
-   * Note: Only falls back one level; "a/b/c" tries "a/b/c" then "a", not "a/b".
+   * Tries exact match first, then progressively shorter parent paths.
+   * e.g., "a/b/c" tries "a/b/c" → "a/b" → "a".
    */
   function findProvidersWithFallback(
     modelType: string
@@ -88,12 +88,13 @@ export const useModelToNodeStore = defineStore('modelToNode', () => {
     const exactMatch = modelToNodeMap.value[modelType]
     if (exactMatch && exactMatch.length > 0) return exactMatch
 
-    const topLevel = modelType.split('/')[0]
-    if (topLevel === modelType) return undefined
-
-    const fallback = modelToNodeMap.value[topLevel]
-
-    if (fallback && fallback.length > 0) return fallback
+    // Try progressively shorter parent paths
+    const segments = modelType.split('/')
+    for (let i = segments.length - 1; i >= 1; i--) {
+      const parentPath = segments.slice(0, i).join('/')
+      const fallback = modelToNodeMap.value[parentPath]
+      if (fallback && fallback.length > 0) return fallback
+    }
 
     return undefined
   }