Add app-server thread/delete API (#25018)

## Why

Clients can archive and unarchive threads today, but there is no
app-server API for permanently removing a thread. Deletion also needs to
cover the full session tree: deleting a main thread should remove
spawned subagent threads and the related local metadata instead of
leaving orphaned rollout files, goals, or subagent state behind.

## What

- Adds the v2 `thread/delete` request and `thread/deleted` notification,
with the response shape kept consistent with `thread/archive`.
- Implements local hard delete for active and archived rollout files.
- Deletes the requested thread's state DB row as the commit point, then
best-effort cleans associated state including spawned descendants,
goals, spawn edges, logs, dynamic tools, and agent job assignments.
- Updates app-server API docs and generated protocol schema/TypeScript
fixtures.

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -324,6 +324,30 @@
           "title": "Thread/archiveRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/v2/RequestId"
+            },
+            "method": {
+              "enum": [
+                "thread/delete"
+              ],
+              "title": "Thread/deleteRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ThreadDeleteParams"
+            }
+          },
+          "required": [
+            "id",
+            "method",
+            "params"
+          ],
+          "title": "Thread/deleteRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -4061,6 +4085,26 @@
           "title": "Thread/archivedNotification",
           "type": "object"
         },
+        {
+          "properties": {
+            "method": {
+              "enum": [
+                "thread/deleted"
+              ],
+              "title": "Thread/deletedNotificationMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ThreadDeletedNotification"
+            }
+          },
+          "required": [
+            "method",
+            "params"
+          ],
+          "title": "Thread/deletedNotification",
+          "type": "object"
+        },
         {
           "properties": {
             "method": {
@@ -16053,6 +16097,37 @@
         "title": "ThreadCompactStartResponse",
         "type": "object"
       },
+      "ThreadDeleteParams": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "threadId": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "threadId"
+        ],
+        "title": "ThreadDeleteParams",
+        "type": "object"
+      },
+      "ThreadDeleteResponse": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "ThreadDeleteResponse",
+        "type": "object"
+      },
+      "ThreadDeletedNotification": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "threadId": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "threadId"
+        ],
+        "title": "ThreadDeletedNotification",
+        "type": "object"
+      },
       "ThreadForkParams": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "description": "There are two ways to fork a thread: 1. By thread_id: load the thread from disk by thread_id and fork it into a new thread. 2. By path: load the thread from disk by path and fork it into a new thread.\n\nIf using a non-empty path, the thread_id param will be ignored. Empty string path values are treated as absent.\n\nPrefer using thread_id whenever possible.",