Resolve MCP server registrations through a catalog (#27634)

## Why

MCP servers currently come from user config, local plugins,
compatibility Apps synthesis, and host extensions. Those sources were
composed by mutating a shared map, leaving registration identity,
precedence, removal, and provenance implicit in assembly order.

Before adding executor-owned MCPs, Codex needs one durable resolution
boundary above `McpConnectionManager`. This PR introduces that boundary
while preserving current server configuration, policy, and runtime
behavior. Executor-scoped registrations and explicit policy layers
remain follow-ups.

## What changed

- Add typed `McpServerRegistration` inputs and an immutable
`ResolvedMcpCatalog` in `codex-mcp`.
- Retain each registration's complete `McpServerConfig`, including its
environment binding, while recording its source and provenance.
- Preserve the existing structural precedence between plugin, config,
compatibility, and ordered extension sources.
- Resolve equal-precedence actions by contribution order; provenance IDs
are used only for diagnostics and cannot affect the winner.
- Preserve extension removals and the existing name-scoped `enabled =
false` veto.
- Report same-tier conflicts with every contender and the final catalog
outcome, including whether the winning action registers or removes the
server.
- Require MCP contributors to provide a stable diagnostic identity.
- Derive materialized server maps and plugin ownership from the resolved
catalog.

`McpConnectionManager`, transport startup, tool calls, and resource
routing continue to consume the same effective `McpServerConfig` values.

## Scope

This PR does not add new MCP capabilities or change user-visible
behavior. It does not add executor plugin discovery, thread-scoped
registrations, dynamic refresh generations, or new user/managed policy
semantics.

## Verification

- Added focused catalog coverage for source precedence, complete
configuration preservation, disabled vetoes, plugin ownership,
contribution-order tie breaking, removal outcomes, and conflict
diagnostics.
- Extended hosted Apps coverage for ordered extension removal and
Apps-disabled hosts with and without the hosted extension installed.
- `cargo check -p codex-mcp --tests -p codex-extension-api -p
codex-core`

codex-rs/codex-mcp/src/lib.rs

@@ -11,6 +11,14 @@ pub use runtime::McpRuntimeContext;
 pub use runtime::SandboxState;
 pub use tools::ToolInfo;
 
+pub use catalog::McpCatalogBuilder;
+pub use catalog::McpServerConflict;
+pub use catalog::McpServerConflictAction;
+pub use catalog::McpServerRegistration;
+pub use catalog::McpServerSource;
+pub use catalog::ResolvedMcpCatalog;
+pub use catalog::ResolvedMcpServer;
+
 pub use mcp::CODEX_APPS_MCP_SERVER_NAME;
 pub use mcp::McpConfig;
 pub use mcp::ToolPluginProvenance;
@@ -57,6 +65,7 @@ pub use mcp::qualified_mcp_tool_name_prefix;
 pub use tools::declared_openai_file_input_param_names;
 
 pub(crate) mod auth_elicitation;
+mod catalog;
 pub(crate) mod codex_apps;
 pub(crate) mod connection_manager;
 pub(crate) mod elicitation;