[codex] Remove string-keyed MCP tool maps (#21454)

## Summary

This PR removes the synthetic `HashMap<String, ToolInfo>` keys from MCP
tool discovery. `McpConnectionManager::list_all_tools()` now returns
normalized `Vec<ToolInfo>`, and downstream code derives identity from
`ToolInfo::canonical_tool_name()`.

The motivation is to keep model-visible tool identity on
`ToolName`/`ToolInfo` instead of parallel string map keys, so future
namespace changes do not have to preserve otherwise-unused lookup keys.

## Changes

- Rename the MCP normalization path from `qualify_tools` to
`normalize_tools_for_model` and return tool values directly.
- Flow MCP tool lists through connectors, plugin injection, router/spec
building, code mode, and tool search as vectors/slices.
- Keep direct/deferred subtraction local to `mcp_tool_exposure`, using
`ToolName` values.
- Update tests to compare `ToolName` instances where MCP identity
matters.

## Validation

- `cargo test -p codex-mcp test_normalize_tools`
- `cargo test -p codex-core mcp_tool_exposure`
- `cargo test -p codex-core
direct_mcp_tools_register_namespaced_handlers`
- `cargo test -p codex-core
search_tool_registers_namespaced_mcp_tool_aliases`
- `just fix -p codex-mcp`
- `just fix -p codex-core`

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

@@ -583,7 +583,7 @@ async fn collect_mcp_server_status_snapshot_from_manager(
     );
 
     let mut tools_by_server = HashMap::<String, HashMap<String, Tool>>::new();
-    for (_qualified_name, tool_info) in tools {
+    for tool_info in tools {
         let raw_tool_name = tool_info.tool.name.to_string();
         let Some(tool) = protocol_tool_from_rmcp_tool(&raw_tool_name, &tool_info.tool) else {
             continue;