feat: node-specific error tab with selection-aware grouping and error overlay (#8956)

## Summary
Enhances the error panel with node-specific views: single-node selection
shows errors grouped by message in compact mode, container nodes
(subgraph/group) expose child errors via a badge and "See Error" button,
and a floating ErrorOverlay appears after execution failure with a
deduplicated summary and quick navigation to the errors tab.

## Changes
- **Consolidate error tab**: Remove `TabError.vue`; merge all error
display into `TabErrors.vue` and drop the separate `error` tab type from
`rightSidePanelStore`
- **Selection-aware grouping**: Single-node selection regroups errors by
message (not `class_type`) and renders `ErrorNodeCard` in compact mode
- **Container node support**: Detect child-node errors in subgraph/group
nodes via execution ID prefix matching; show error badge and "See Error"
button in `SectionWidgets`
- **ErrorOverlay**: New floating card shown after execution failure with
deduplicated error messages, "Dismiss" and "See Errors" actions;
`isErrorOverlayOpen` / `showErrorOverlay` / `dismissErrorOverlay` added
to `executionStore`
- **Refactor**: Centralize error ID collection in `executionStore`
(`allErrorExecutionIds`, `hasInternalErrorForNode`); split `errorGroups`
into `allErrorGroups` (unfiltered) and `tabErrorGroups`
(selection-filtered); move `ErrorOverlay` business logic into
`useErrorGroups`

## Review Focus
- `useErrorGroups.ts`: split into `allErrorGroups` / `tabErrorGroups`
and the new `filterBySelection` parameter flow
- `executionStore.ts`: `hasInternalErrorForNode` helper and
`allErrorExecutionIds` computed
- `ErrorOverlay.vue`: integration with `executionStore` overlay state
and `useErrorGroups`

## Screenshots
<img width="853" height="461" alt="image"
src="https://github.com/user-attachments/assets/a49ab620-4209-4ae7-b547-fba13da0c633"
/>
<img width="854" height="203" alt="image"
src="https://github.com/user-attachments/assets/c119da54-cd78-4e7a-8b7a-456cfd348f1d"
/>
<img width="497" height="361" alt="image"
src="https://github.com/user-attachments/assets/74b16161-cf45-454b-ae60-24922fe36931"
/>

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: github-actions <github-actions@github.com>

src/locales/en/main.json

@@ -1381,6 +1381,7 @@
     "Execution": "Execution",
     "PLY": "PLY",
     "Workspace": "Workspace",
+    "Error System": "Error System",
     "Other": "Other",
     "Secrets": "Secrets",
     "Error System": "Error System"
@@ -3010,6 +3011,7 @@
     "hideAdvancedInputsButton": "Hide advanced inputs",
     "errors": "Errors",
     "noErrors": "No errors",
+    "executionErrorOccurred": "An error occurred during execution. Check the Errors tab for details.",
     "enterSubgraph": "Enter subgraph",
     "seeError": "See Error",
     "promptErrors": {
@@ -3018,6 +3020,12 @@
       },
       "no_prompt": {
         "desc": "The workflow data sent to the server is empty. This may be an unexpected system error."
+      },
+      "server_error_local": {
+        "desc": "The server encountered an unexpected error. Please check the server logs."
+      },
+      "server_error_cloud": {
+        "desc": "The server encountered an unexpected error. Please try again later."
       }
     },
     "errorHelp": "For more help, {github} or {support}",
@@ -3026,6 +3034,10 @@
     "resetToDefault": "Reset to default",
     "resetAllParameters": "Reset all parameters"
   },
+  "errorOverlay": {
+    "errorCount": "{count} ERRORS | {count} ERROR | {count} ERRORS",
+    "seeErrors": "See Errors"
+  },
   "help": {
     "recentReleases": "Recent releases",
     "helpCenterMenu": "Help Center Menu"