Migrate tui to use UserTurn (#9497)

- `tui/` and `tui2/` submit `Op::UserTurn` and own full turn context
(cwd/approval/sandbox/model/etc.).
- `Op::UserInput` is documented as legacy in `codex-protocol` (doc-only;
no `#[deprecated]` to avoid `-D warnings` fallout).
- Remove obsolete `#[allow(deprecated)]` and the unused `ConversationId`
alias/re-export.

codex-rs/protocol/src/protocol.rs

@@ -83,7 +83,10 @@ pub enum Op {
     /// This server sends [`EventMsg::TurnAborted`] in response.
     Interrupt,
 
-    /// Input from the user
+    /// Legacy user input.
+    ///
+    /// Prefer [`Op::UserTurn`] so the caller provides full turn context
+    /// (cwd/approval/sandbox/model/etc.) for each turn.
     UserInput {
         /// User input items, see `InputItem`
         items: Vec<UserInput>,
@@ -131,7 +134,8 @@ pub enum Op {
     ///
     /// All fields are optional; when omitted, the existing value is preserved.
     /// This does not enqueue any input – it only updates defaults used for
-    /// future `UserInput` turns.
+    /// turns that rely on persistent session-level context (for example,
+    /// [`Op::UserInput`]).
     OverrideTurnContext {
         /// Updated `cwd` for sandbox/tool calls.
         #[serde(skip_serializing_if = "Option::is_none")]