TUI: Add session resume picker (--resume) and quick resume (--continue) (#3135)

Adds a TUI resume flow with an interactive picker and quick resume.

- CLI: 
  - --resume / -r: open picker to resume a prior session
  - --continue   / -l: resume the most recent session (no picker)
- Behavior on resume: initial history is replayed, welcome banner
hidden, and the first redraw is suppressed to avoid flicker.
- Implementation:
- New tui/src/resume_picker.rs (paginated listing via
RolloutRecorder::list_conversations)
  - App::run accepts ResumeSelection; resumes from disk when requested
- ChatWidget refactor with ChatWidgetInit and new_from_existing; replays
initial messages
- Tests: cover picker sorting/preview extraction and resumed-history
rendering.
- Docs: getting-started updated with flags and picker usage.



https://github.com/user-attachments/assets/1bb6469b-e5d1-42f6-bec6-b1ae6debda3b

docs/getting-started.md

@@ -10,6 +10,18 @@
 
 Key flags: `--model/-m`, `--ask-for-approval/-a`.
 
+Resume options:
+
+- `--resume`: open an interactive picker of recent sessions (shows a preview of the first real user message). Conflicts with `--continue`.
+- `--continue`: resume the most recent session without showing the picker (falls back to starting fresh if none exist). Conflicts with `--resume`.
+
+Examples:
+
+```shell
+codex --resume
+codex --continue
+```
+
 ### Running with a prompt as input
 
 You can also run Codex CLI with a prompt as input: