chore(assets): scripted screenshot pipeline

docs/tui-ux-playbook.md

@@ -176,3 +176,16 @@ When modifying TUI UX or keybindings:
 
 Keeping these steps in sync ensures Owlen’s keyboard-first UX remains
 predictable, accessible, and discoverable.
+
+## 8. Screenshot Pipeline
+
+Use the scripted pipeline to regenerate gallery assets and documentation
+illustrations:
+
+- `cargo xtask screenshots` emits ANSI dumps under `images/generated` and, by
+  default, converts them to PNG with `chafa`. Pass `--no-png` to skip PNG
+  rendering or `--chafa /path/to/chafa` to override the binary. Each scene is
+  deterministic—no network calls—and mirrors the regression snapshots.
+- The pipeline reuses the same stub provider harness as the snapshot tests, so
+  new scenes should be added in tandem with `chat_snapshots.rs` to keep visual
+  regression coverage and documentation imagery aligned.