Split MCP connection modules (#19725)

## Why

The MCP connection manager module had grown to mix orchestration, RMCP
client startup, elicitation handling, Codex Apps cache and naming
behavior, tool qualification and filtering, and runtime data. The
previous stacked PRs split these responsibilities incrementally; this PR
collapses that work into one self-contained refactor on latest main.

## What changed

- Move McpConnectionManager into connection_manager.rs.
- Move RMCP client lifecycle, startup, and uncached tool listing into
rmcp_client.rs.
- Move elicitation request tracking and policy handling into
elicitation.rs.
- Move Codex Apps cache, key, filtering, and naming helpers into
codex_apps.rs.
- Rename the tool-name helper module to tools.rs and move ToolInfo, tool
filtering, schema masking, and qualification there.
- Move runtime and sandbox shared types into runtime.rs.
- Preserve latest main PermissionProfile-based MCP elicitation
auto-approval behavior.

## Verification

- just fmt
- cargo check -p codex-mcp
- cargo check -p codex-mcp --tests
- cargo check -p codex-core

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/codex-mcp/src/mcp/mod.rs

@@ -34,9 +34,9 @@ use rmcp::model::ReadResourceRequestParams;
 use rmcp::model::ReadResourceResult;
 use serde_json::Value;
 
-use crate::mcp_connection_manager::McpConnectionManager;
-use crate::mcp_connection_manager::McpRuntimeEnvironment;
-use crate::mcp_connection_manager::codex_apps_tools_cache_key;
+use crate::codex_apps::codex_apps_tools_cache_key;
+use crate::connection_manager::McpConnectionManager;
+use crate::runtime::McpRuntimeEnvironment;
 
 pub const CODEX_APPS_MCP_SERVER_NAME: &str = "codex_apps";
 const MCP_TOOL_NAME_PREFIX: &str = "mcp";