Option to Notify Workspace Owner When Usage Limit is Reached (#16969)

## Summary
- Replace the manual `/notify-owner` flow with an inline confirmation
prompt when a usage-based workspace member hits a credits-depleted
limit.
- Fetch the current workspace role from the live ChatGPT
`accounts/check/v4-2023-04-27` endpoint so owner/member behavior matches
the desktop and web clients.
- Keep owner, member, and spend-cap messaging distinct so we only offer
the owner nudge when the workspace is actually out of credits.

## What Changed
- `backend-client`
- Added a typed fetch for the current account role from
`accounts/check`.
  - Mapped backend role values into a Rust workspace-role enum.
- `app-server` and protocol
  - Added `workspaceRole` to `account/read` and `account/updated`.
- Derived `isWorkspaceOwner` from the live role, with a fallback to the
cached token claim when the role fetch is unavailable.
- `tui`
  - Removed the explicit `/notify-owner` slash command.
- When a member is blocked because the workspace is out of credits, the
error now prompts:
- `Your workspace is out of credits. Request more from your workspace
owner? [y/N]`
  - Choosing `y` sends the existing owner-notification request.
- Choosing `n`, pressing `Esc`, or accepting the default selection
dismisses the prompt without sending anything.
- Selection popups now honor explicit item shortcuts, which is how the
`y` / `n` interaction is wired.

## Reviewer Notes
- The main behavior change is scoped to usage-based workspace members
whose workspace credits are depleted.
- Spend-cap reached should not show the owner-notification prompt.
- Owners and admins should continue to see `/usage` guidance instead of
the member prompt.
- The live role fetch is best-effort; if it fails, we fall back to the
existing token-derived ownership signal.

## Testing
- Manual verification
  - Workspace owner does not see the member prompt.
- Workspace member with depleted credits sees the confirmation prompt
and can send the nudge with `y`.
- Workspace member with spend cap reached does not see the
owner-notification prompt.

### Workspace member out of usage

https://github.com/user-attachments/assets/341ac396-eff4-4a7f-bf0c-60660becbea1

### Workspace owner
<img width="1728" height="1086" alt="Screenshot 2026-04-09 at 11 48
22 AM"
src="https://github.com/user-attachments/assets/06262a45-e3fc-4cc4-8326-1cbedad46ed6"
/>

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -2562,6 +2562,17 @@
       ],
       "type": "object"
     },
+    "ThreadAddCreditsNudgeEmailParams": {
+      "properties": {
+        "threadId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "threadId"
+      ],
+      "type": "object"
+    },
     "ThreadArchiveParams": {
       "properties": {
         "threadId": {
@@ -3809,6 +3820,30 @@
       "title": "Thread/shellCommandRequest",
       "type": "object"
     },
+    {
+      "properties": {
+        "id": {
+          "$ref": "#/definitions/RequestId"
+        },
+        "method": {
+          "enum": [
+            "thread/addCreditsNudgeEmail"
+          ],
+          "title": "Thread/addCreditsNudgeEmailRequestMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/ThreadAddCreditsNudgeEmailParams"
+        }
+      },
+      "required": [
+        "id",
+        "method",
+        "params"
+      ],
+      "title": "Thread/addCreditsNudgeEmailRequest",
+      "type": "object"
+    },
     {
       "properties": {
         "id": {