fix(settings): toast and block save when node settings fail to load (#1654)

* fix(settings): toast and block save when node settings fail to load

Failed GET /settings no longer seeds defaults as the dirty baseline. Shared
loader pins node identity, shows an error callout until an authoritative load
succeeds, and keeps Save disabled across all eight node-scoped sections.

* test(settings): cover load-failure toast and App Store refresh pin

Remove the incorrect settings-load-failure docs image. Assert toast ownership for current vs stale/aborted loads, and pin App Store cache refresh to the PATCH node across a mid-save switch.

* fix(settings): reject malformed settings bodies and skip pre-node bootstrap load

Treat non-object 200 /settings payloads as load failures so null or array bodies cannot seed editable defaults. Do not fetch or toast while the active node id is still undefined, so hard refresh settles to a single failure toast.

docs/reference/settings.mdx

@@ -51,6 +51,8 @@ Click **Filter** at the top of the sidebar, or press `Ctrl+K` / `⌘K` while the
 
 For node-scoped sections the masthead replaces the **SCOPE** pill with a **NODE** pill showing the active node name. Switch the active node from the top bar's **Switch node** button to edit a different node's per-node settings.
 
+If settings for the active node fail to load, Sencho shows an error and keeps Save unavailable until an authoritative load for that node succeeds.
+
 <Frame>
   <img src="/images/settings/settings-node-scope.png" alt="Host Alerts section showing the NODE pill in the masthead" />
 </Frame>