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/src/protocol/v2/item.rs

@@ -396,6 +396,9 @@ pub struct McpToolCallAppContext {
     pub connector_id: String,
     pub link_id: Option<String>,
     pub resource_uri: Option<String>,
+    pub app_name: Option<String>,
+    pub template_id: Option<String>,
+    pub action_name: Option<String>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
@@ -895,6 +898,9 @@ impl From<CoreTurnItem> for ThreadItem {
                         connector_id,
                         link_id: mcp.link_id,
                         resource_uri: mcp.mcp_app_resource_uri.clone(),
+                        app_name: mcp.app_name,
+                        template_id: mcp.template_id,
+                        action_name: mcp.action_name,
                     }),
                     mcp_app_resource_uri: mcp.mcp_app_resource_uri,
                     plugin_id: mcp.plugin_id,