feat: classify missing nodes by replacement availability (#8483)

## Summary
- Extend `MissingNodeType` with `isReplaceable` and `replacement` fields
- Classify missing nodes by checking
`nodeReplacementStore.getReplacementFor()` during graph load
- Wrap hardcoded node patches (T2IAdapterLoader, ConditioningAverage,
etc.) in `if (!isEnabled)` guard so they only run when node replacement
setting is disabled
- Change `useNodeReplacementStore().load()` from fire-and-forget
(`void`) to `await` so replacement data is available before missing node
detection
- Fix guard condition order in `nodeReplacementStore.load()`: check
`isEnabled` before `isLoaded`
- Align `InputMap` types with actual API response (flat
`old_id`/`set_value` fields instead of nested `assign` wrapper)

## Test plan
- [x] Load workflow with deprecated nodes (T2IAdapterLoader,
Load3DAnimation, SDV_img2vid_Conditioning)
- [x] Verify missing nodes are classified with `isReplaceable: true` and
`replacement` object
- [x] Verify hardcoded patches only run when node replacement setting is
OFF
- [x] Verify `nodeReplacementStore.load()` is not called when setting is
disabled
- [x] Unit tests pass (`nodeReplacementStore.test.ts` - 16 tests)
- [x] Typecheck passes

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

src/platform/nodeReplacement/nodeReplacementStore.test.ts

@@ -247,5 +247,15 @@ describe('useNodeReplacementStore', () => {
 
       expect(fetchNodeReplacements).toHaveBeenCalledOnce()
     })
+
+    it('should not call API when setting is disabled', async () => {
+      vi.mocked(fetchNodeReplacements).mockResolvedValue(mockReplacements)
+      store = createStore(false)
+
+      await store.load()
+
+      expect(fetchNodeReplacements).not.toHaveBeenCalled()
+      expect(store.isLoaded).toBe(false)
+    })
   })
 })

src/platform/nodeReplacement/nodeReplacementStore.ts

@@ -15,8 +15,7 @@ export const useNodeReplacementStore = defineStore('nodeReplacement', () => {
   )
 
   async function load() {
-    if (isLoaded.value || !isEnabled.value) return
-
+    if (!isEnabled.value || isLoaded.value) return
     try {
       replacements.value = await fetchNodeReplacements()
       isLoaded.value = true

src/platform/nodeReplacement/types.ts

@@ -1,17 +1,14 @@
-interface InputAssignOldId {
-  assign_type: 'old_id'
+interface InputMapOldId {
+  new_id: string
   old_id: string
 }
 
-interface InputAssignSetValue {
-  assign_type: 'set_value'
-  value: unknown
+interface InputMapSetValue {
+  new_id: string
+  set_value: unknown
 }
 
-interface InputMap {
-  new_id: string
-  assign: InputAssignOldId | InputAssignSetValue
-}
+type InputMap = InputMapOldId | InputMapSetValue
 
 interface OutputMap {
   new_idx: number