Expose MCP app identity in app context (#29934)

## Why

MCP tool-call events need to expose trusted app identity and action
metadata directly so v2 clients do not have to infer it from tool names
or resource URIs.

## What changed

- Add optional `appName`, `templateId`, and `actionName` fields to MCP
tool-call `appContext`.
- Populate `appName` and `templateId` from trusted Codex Apps metadata,
and derive `actionName` from the trusted app resource metadata.
- Preserve all three fields through core events, legacy protocol events,
persisted thread history, resume redaction, and app-server v2 responses.
- Document the public `appContext` fields in
`codex-rs/app-server/README.md`.
- Regenerate app-server JSON and TypeScript schemas and add coverage for
serialization, persistence, redaction, and metadata propagation.

## Validation

- `just test -p codex-app-server-protocol mcp_tool_call`
- `just test -p codex-core
mcp_tool_call_item_metadata_only_trusts_codex_apps_identity
mcp_tool_call_item_includes_app_identity`
- `just write-app-server-schema`

---------

Co-authored-by: Martin Au-Yeung <280153141+martinauyeung-oai@users.noreply.github.com>

codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json

@@ -463,6 +463,18 @@
     },
     "McpToolCallAppContext": {
       "properties": {
+        "actionName": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
+        "appName": {
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "connectorId": {
           "type": "string"
         },
@@ -477,6 +489,12 @@
             "string",
             "null"
           ]
+        },
+        "templateId": {
+          "type": [
+            "string",
+            "null"
+          ]
         }
       },
       "required": [