feat(app-server): include turns page on thread resume (#23534)

## Summary

The client currently calls `thread/resume` to establish live updates and
immediately follows it with `thread/turns/list` to hydrate recent turns.
This lets `thread/resume` return that page directly, eliminating a round
trip and the ordering/deduplication gap between the two calls.

Experimental clients opt in with `initialTurnsPage: { limit,
sortDirection, itemsView }`. The response returns `initialTurnsPage` as
a `TurnsPage`, including cursors for paging further back in history.
Keeping the controls in a nested opt-in object provides the useful
`thread/turns/list` knobs without spreading page-specific parameters
across `thread/resume`.

## Verification

- `just fmt`
- `just write-app-server-schema --experimental`
- `just write-app-server-schema`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server
thread_resume_initial_turns_page_matches_requested_turns_list_page
--tests`
- `cargo test -p codex-app-server
thread_resume_rejoins_running_thread_even_with_override_mismatch
--tests`
- `just fix -p codex-app-server-protocol -p codex-app-server`

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

@@ -3543,6 +3543,42 @@
         }
       ]
     },
+    "ThreadResumeInitialTurnsPageParams": {
+      "properties": {
+        "itemsView": {
+          "anyOf": [
+            {
+              "$ref": "#/definitions/TurnItemsView"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "description": "How much item detail to include for each returned turn; defaults to summary."
+        },
+        "limit": {
+          "description": "Optional turn page size.",
+          "format": "uint32",
+          "minimum": 0.0,
+          "type": [
+            "integer",
+            "null"
+          ]
+        },
+        "sortDirection": {
+          "anyOf": [
+            {
+              "$ref": "#/definitions/SortDirection"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "description": "Optional turn pagination direction; defaults to descending."
+        }
+      },
+      "type": "object"
+    },
     "ThreadResumeParams": {
       "description": "There are three ways to resume a thread: 1. By thread_id: load the thread from disk by thread_id and resume it. 2. By history: instantiate the thread from memory and resume it. 3. By path: load the thread from disk by path and resume it.\n\nFor non-running threads, the precedence is: history > non-empty path > thread_id. If using history or a non-empty path for a non-running thread, the thread_id param will be ignored.\n\nIf thread_id identifies a running thread, app-server rejoins that thread and treats a non-empty path as a consistency check against the active rollout path. Empty string path values are treated as absent.\n\nPrefer using thread_id whenever possible.",
       "properties": {