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/ServerNotification.json

@@ -51,6 +51,12 @@
             }
           ]
         },
+        "isWorkspaceOwner": {
+          "type": [
+            "boolean",
+            "null"
+          ]
+        },
         "planType": {
           "anyOf": [
             {
@@ -60,10 +66,89 @@
               "type": "null"
             }
           ]
+        },
+        "workspaceRole": {
+          "anyOf": [
+            {
+              "$ref": "#/definitions/WorkspaceRole"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "type": "object"
     },
+    "AddCreditsNudgeEmailNotification": {
+      "properties": {
+        "result": {
+          "$ref": "#/definitions/AddCreditsNudgeEmailResult"
+        },
+        "threadId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "result",
+        "threadId"
+      ],
+      "type": "object"
+    },
+    "AddCreditsNudgeEmailResult": {
+      "oneOf": [
+        {
+          "properties": {
+            "status": {
+              "enum": [
+                "sent"
+              ],
+              "title": "SentAddCreditsNudgeEmailResultStatus",
+              "type": "string"
+            }
+          },
+          "required": [
+            "status"
+          ],
+          "title": "SentAddCreditsNudgeEmailResult",
+          "type": "object"
+        },
+        {
+          "properties": {
+            "status": {
+              "enum": [
+                "cooldownActive"
+              ],
+              "title": "CooldownActiveAddCreditsNudgeEmailResultStatus",
+              "type": "string"
+            }
+          },
+          "required": [
+            "status"
+          ],
+          "title": "CooldownActiveAddCreditsNudgeEmailResult",
+          "type": "object"
+        },
+        {
+          "properties": {
+            "message": {
+              "type": "string"
+            },
+            "status": {
+              "enum": [
+                "failed"
+              ],
+              "type": "string"
+            }
+          },
+          "required": [
+            "message",
+            "status"
+          ],
+          "type": "object"
+        }
+      ]
+    },
     "AgentMessageDeltaNotification": {
       "properties": {
         "delta": {
@@ -2045,6 +2130,16 @@
               "type": "null"
             }
           ]
+        },
+        "spendControl": {
+          "anyOf": [
+            {
+              "$ref": "#/definitions/SpendControlSnapshot"
+            },
+            {
+              "type": "null"
+            }
+          ]
         }
       },
       "type": "object"
@@ -2244,6 +2339,17 @@
       "description": "Notification emitted when watched local skill files change.\n\nTreat this as an invalidation signal and re-run `skills/list` with the client's current parameters when refreshed skill metadata is needed.",
       "type": "object"
     },
+    "SpendControlSnapshot": {
+      "properties": {
+        "reached": {
+          "type": "boolean"
+        }
+      },
+      "required": [
+        "reached"
+      ],
+      "type": "object"
+    },
     "SubAgentSource": {
       "oneOf": [
         {
@@ -4028,6 +4134,14 @@
         "samplePaths"
       ],
       "type": "object"
+    },
+    "WorkspaceRole": {
+      "enum": [
+        "account-owner",
+        "account-admin",
+        "standard-user"
+      ],
+      "type": "string"
     }
   },
   "description": "Notification sent from the server to the client.",
@@ -4655,6 +4769,26 @@
       "title": "Account/rateLimits/updatedNotification",
       "type": "object"
     },
+    {
+      "properties": {
+        "method": {
+          "enum": [
+            "account/addCreditsNudgeEmail/completed"
+          ],
+          "title": "Account/addCreditsNudgeEmail/completedNotificationMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/AddCreditsNudgeEmailNotification"
+        }
+      },
+      "required": [
+        "method",
+        "params"
+      ],
+      "title": "Account/addCreditsNudgeEmail/completedNotification",
+      "type": "object"
+    },
     {
       "properties": {
         "method": {