Add session resume to the agent command center (#42419)

## What changed

- Add a configurable `agents.resume` action, bound to `Ctrl+O` by default, that opens the session resume picker from the agent command center.
- Preserve command-center state when the picker is cancelled, and preserve per-thread composer and queued-input state when switching sessions.
- Keep resume failures within the command-center flow and wrap footer shortcuts on narrow terminals.

## Testing

- Add coverage for picker cancellation, active-session selection, resume failures, per-thread input restoration, custom keybindings, and narrow footer layout.

GitOrigin-RevId: 59159f838a0c642200cd164e3af45b0971d29bf8

codex-rs/core/config.schema.json

@@ -3858,6 +3858,7 @@
             "agents": {
               "new_task": null,
               "rename": null,
+              "resume": null,
               "search": null,
               "stop": null,
               "toggle_grouping": null
@@ -4164,6 +4165,14 @@
           ],
           "description": "Rename the selected task."
         },
+        "resume": {
+          "allOf": [
+            {
+              "$ref": "#/definitions/KeybindingsSpec"
+            }
+          ],
+          "description": "Open the session resume picker."
+        },
         "search": {
           "allOf": [
             {
@@ -4631,6 +4640,7 @@
           "default": {
             "new_task": null,
             "rename": null,
+            "resume": null,
             "search": null,
             "stop": null,
             "toggle_grouping": null