Move message history out of core (#21278)

## Why

Message history was implemented inside `codex-core` and surfaced through
core protocol ops and `SessionConfiguredEvent` fields even though the
current consumer is TUI-local prompt recall. That made core own UI
history persistence and exposed `history_log_id` / `history_entry_count`
through surfaces that app-server and other clients do not need.

This change moves message history persistence out of core and keeps the
recall plumbing local to the TUI.

## What changed

- Added a new `codex-message-history` crate for appending, looking up,
trimming, and reading metadata from `history.jsonl`.
- Removed core protocol history ops/events: `AddToHistory`,
`GetHistoryEntryRequest`, and `GetHistoryEntryResponse`.
- Removed `history_log_id` and `history_entry_count` from
`SessionConfiguredEvent` and updated exec/MCP/test fixtures accordingly.
- Updated the TUI to dispatch local app events for message-history
append/lookup and keep its persistent-history metadata in TUI session
state.

## Validation

- `cargo test -p codex-message-history -p codex-protocol`
- `cargo test -p codex-exec event_processor_with_json_output`
- `cargo test -p codex-mcp-server outgoing_message`
- `cargo test -p codex-tui`
- `just fix -p codex-message-history -p codex-protocol -p codex-core -p
codex-tui -p codex-exec -p codex-mcp-server`

codex-rs/app-server-client/src/lib.rs

@@ -72,12 +72,9 @@ pub mod legacy_core {
     pub use codex_core::DEFAULT_AGENTS_MD_FILENAME;
     pub use codex_core::LOCAL_AGENTS_MD_FILENAME;
     pub use codex_core::McpManager;
-    pub use codex_core::append_message_history_entry;
     pub use codex_core::check_execpolicy_for_warnings;
     pub use codex_core::format_exec_policy_error_with_source;
     pub use codex_core::grant_read_root_non_elevated;
-    pub use codex_core::lookup_message_history_entry;
-    pub use codex_core::message_history_metadata;
     pub use codex_core::web_search_detail;
 
     pub mod config {