Revert thread recencyAt for sidebar ordering (#28655)

## Why

Revert #27910 to remove the newly introduced thread `recencyAt`
persistence and API behavior from `main`.

## What changed

This reverts commit `fac3158c2a783095768076489815f361fa9b0db4`,
including the state migration, thread-store propagation, app-server API
surface, generated schemas, and related tests.

## Validation

Not run before opening; relying on CI for the initial fast signal.

codex-rs/rollout/src/state_db.rs

@@ -290,10 +290,7 @@ fn cursor_to_anchor(cursor: Option<&Cursor>) -> Option<codex_state::Anchor> {
     let millis = cursor.timestamp().unix_timestamp_nanos() / 1_000_000;
     let millis = i64::try_from(millis).ok()?;
     let ts = chrono::DateTime::<Utc>::from_timestamp_millis(millis)?;
-    Some(codex_state::Anchor {
-        ts,
-        id: cursor.thread_id(),
-    })
+    Some(codex_state::Anchor { ts })
 }
 
 pub fn normalize_cwd_for_state_db(cwd: &Path) -> PathBuf {
@@ -339,7 +336,6 @@ pub async fn list_thread_ids_db(
             match sort_key {
                 ThreadSortKey::CreatedAt => codex_state::SortKey::CreatedAt,
                 ThreadSortKey::UpdatedAt => codex_state::SortKey::UpdatedAt,
-                ThreadSortKey::RecencyAt => codex_state::SortKey::RecencyAt,
             },
             allowed_sources.as_slice(),
             model_providers.as_deref(),
@@ -405,7 +401,6 @@ pub async fn list_threads_db(
         sort_key: match sort_key {
             ThreadSortKey::CreatedAt => codex_state::SortKey::CreatedAt,
             ThreadSortKey::UpdatedAt => codex_state::SortKey::UpdatedAt,
-            ThreadSortKey::RecencyAt => codex_state::SortKey::RecencyAt,
         },
         sort_direction: match sort_direction {
             SortDirection::Asc => codex_state::SortDirection::Asc,