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/tui/src/app_command.rs

@@ -103,13 +103,6 @@ pub(crate) enum AppCommand {
     Review {
         target: ReviewTarget,
     },
-    AddToHistory {
-        text: String,
-    },
-    GetHistoryEntryRequest {
-        offset: usize,
-        log_id: u64,
-    },
     ApproveGuardianDeniedAction {
         event: GuardianAssessmentEvent,
     },
@@ -275,14 +268,6 @@ impl AppCommand {
         Self::Review { target }
     }
 
-    pub(crate) fn add_to_history(text: String) -> Self {
-        Self::AddToHistory { text }
-    }
-
-    pub(crate) fn history_lookup(offset: usize, log_id: u64) -> Self {
-        Self::GetHistoryEntryRequest { offset, log_id }
-    }
-
     pub(crate) fn approve_guardian_denied_action(event: GuardianAssessmentEvent) -> Self {
         Self::ApproveGuardianDeniedAction { event }
     }