[apps] Add apps MCP path override (#20231)

Summary

- Add `[features.apps_mcp_path_override]` config with a `path` field for
overriding only the built-in apps MCP path.
- Keep existing host/base URL derivation unchanged and append the
configured path after that base.
- Regenerate the config schema with the custom feature-config case.

Test Plan

- Not run for latest revision; only `just fmt` and `just
write-config-schema` were run.
- Earlier revision: `cargo test -p codex-features`
- Earlier revision: `cargo test -p codex-mcp`

codex-rs/core/config.schema.json

@@ -218,6 +218,18 @@
       },
       "type": "object"
     },
+    "AppsMcpPathOverrideConfigToml": {
+      "additionalProperties": false,
+      "properties": {
+        "enabled": {
+          "type": "boolean"
+        },
+        "path": {
+          "type": "string"
+        }
+      },
+      "type": "object"
+    },
     "AskForApproval": {
       "description": "Determines the conditions under which the user is consulted to approve running the command proposed by Codex.",
       "oneOf": [
@@ -355,6 +367,9 @@
             "apps": {
               "type": "boolean"
             },
+            "apps_mcp_path_override": {
+              "$ref": "#/definitions/FeatureToml_for_AppsMcpPathOverrideConfigToml"
+            },
             "browser_use": {
               "type": "boolean"
             },
@@ -705,6 +720,16 @@
       },
       "type": "object"
     },
+    "FeatureToml_for_AppsMcpPathOverrideConfigToml": {
+      "anyOf": [
+        {
+          "type": "boolean"
+        },
+        {
+          "$ref": "#/definitions/AppsMcpPathOverrideConfigToml"
+        }
+      ]
+    },
     "FeatureToml_for_MultiAgentV2ConfigToml": {
       "anyOf": [
         {
@@ -3297,6 +3322,9 @@
         "apps": {
           "type": "boolean"
         },
+        "apps_mcp_path_override": {
+          "$ref": "#/definitions/FeatureToml_for_AppsMcpPathOverrideConfigToml"
+        },
         "browser_use": {
           "type": "boolean"
         },