feat(tui): codex-style input, history, bang commands, single-line status bar

- Arrow-key input history (up/down with multiline awareness)
- Bang shell commands via ! prefix (requires --yolo)
- Codex-style input bar with mode indicator (R/Y/⌘)
- Command palette virtual scrolling
- Multiline input viewport fix
- Merged model pills + footer into single status line
- Removed shift+enter (wait for TUI library support)
- Removed default footer hints

README.md

@@ -100,11 +100,13 @@ go run . [flags]
 ## TUI Controls
 
 - `enter` sends the message.
-- `ctrl+j` or `alt+enter` inserts a newline.
+- `ctrl+j` inserts a newline.
+- `up` recalls the previous input; `ctrl+p` / `ctrl+n` navigate input history.
 - The input starts at one line and grows up to six lines.
 - `page up` / `page down` scrolls the transcript.
 - `esc` cancels a running response.
 - Type `/` to show available commands.
+- In `--yolo` mode, type `! <command>` to run a shell command from the configured working directory.
 
 Slash commands:
 
@@ -116,6 +118,7 @@ Slash commands:
 - `/model` shows current provider, model, thinking, and switch usage.
 - `/model provider <name>` switches provider for the current session.
 - `/model model <name>` or `/model <name>` switches model for the current session.
+  In the TUI, type `/model ` or `/model model ` to choose from configured model IDs in the candidate palette.
 - `/model thinking <none|middle|high|xhigh|max>` changes thinking for the current session.
 - `/sessions` lists saved sessions.
 - `/resume [id]` resumes by ID or opens an interactive picker.