[app-server] feat: v2 Thread APIs (#6214)

Implements:
```
thread/list
thread/start
thread/resume
thread/archive
```

along with their integration tests. These are relatively light wrappers
around the existing core logic, and changes to core logic are minimal.

However, an improvement made for developer ergonomics:
- `thread/start` and `thread/resume` automatically attaches a
conversation listener internally, so clients don't have to make a
separate `AddConversationListener` call like they do today.

For consistency, also updated `model/list` and `feedback/upload` (naming
conventions, list API params).

codex-rs/core/src/lib.rs

@@ -75,6 +75,7 @@ pub use rollout::find_conversation_path_by_id_str;
 pub use rollout::list::ConversationItem;
 pub use rollout::list::ConversationsPage;
 pub use rollout::list::Cursor;
+pub use rollout::list::parse_cursor;
 pub use rollout::list::read_head_for_summary;
 mod function_tool;
 mod state;

codex-rs/core/src/rollout/list.rs

@@ -273,7 +273,7 @@ async fn traverse_directories_for_paths(
 /// Pagination cursor token format: "<file_ts>|<uuid>" where `file_ts` matches the
 /// filename timestamp portion (YYYY-MM-DDThh-mm-ss) used in rollout filenames.
 /// The cursor orders files by timestamp desc, then UUID desc.
-fn parse_cursor(token: &str) -> Option<Cursor> {
+pub fn parse_cursor(token: &str) -> Option<Cursor> {
     let (file_ts, uuid_str) = token.split_once('|')?;
 
     let Ok(uuid) = Uuid::parse_str(uuid_str) else {