[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/codex_apps.rs

@@ -5,7 +5,6 @@
 //! connector allow-list filtering, and the normalization that turns app
 //! connector/tool metadata into model-visible MCP callable names.
 
-use std::collections::HashMap;
 use std::path::PathBuf;
 use std::time::Instant;
 
@@ -38,16 +37,6 @@ pub fn codex_apps_tools_cache_key(auth: Option<&CodexAuth>) -> CodexAppsToolsCac
     }
 }
 
-pub fn filter_non_codex_apps_mcp_tools_only(
-    mcp_tools: &HashMap<String, ToolInfo>,
-) -> HashMap<String, ToolInfo> {
-    mcp_tools
-        .iter()
-        .filter(|(_, tool)| tool.server_name != CODEX_APPS_MCP_SERVER_NAME)
-        .map(|(name, tool)| (name.clone(), tool.clone()))
-        .collect()
-}
-
 #[derive(Clone)]
 pub(crate) struct CodexAppsToolsCacheContext {
     pub(crate) codex_home: PathBuf,