Add redo support to Vim composer history (#42140)

## What changed

- Add a bounded redo stack for complete composer drafts, including paste payloads and image attachments. `Ctrl+R` now reapplies the last undone edit in Vim normal mode, while new edits clear stale redo history.
- Add the configurable `vim_normal.redo` action to the keymap schema and picker. Preserve reverse prompt-history search in Vim insert mode and non-Vim mode, and honor explicitly configured bindings.
- Keep pending edit snapshots outside the shared undo/redo byte budget so canceled commands cannot evict committed history.

## Testing

- Cover grouped edits, Vim searches, direct draft changes, history limits, empty redo stacks, and custom or unbound shortcuts.

GitOrigin-RevId: 0cf5bb376ff865ddc0a77705dcb322ef6b57b3a3

codex-rs/core/config.schema.json

@@ -3944,6 +3944,7 @@
               "open_line_above": null,
               "open_line_below": null,
               "paste_after": null,
+              "redo": null,
               "repeat_last_change": null,
               "replace_char": null,
               "start_change_operator": null,
@@ -4771,6 +4772,7 @@
             "open_line_above": null,
             "open_line_below": null,
             "paste_after": null,
+            "redo": null,
             "repeat_last_change": null,
             "replace_char": null,
             "start_change_operator": null,
@@ -5234,6 +5236,14 @@
           ],
           "description": "Paste after cursor (`p`)."
         },
+        "redo": {
+          "allOf": [
+            {
+              "$ref": "#/definitions/KeybindingsSpec"
+            }
+          ],
+          "description": "Redo the last undone edit (`ctrl-r`)."
+        },
         "repeat_last_change": {
           "allOf": [
             {