fix(tui): add vertical scrolling to Editor when content exceeds terminal height

The Editor component now accepts TUI as the first constructor parameter,
enabling it to query terminal dimensions. When content exceeds available
height, the editor scrolls vertically keeping the cursor visible.

Features:
- Max editor height is 30% of terminal rows (minimum 5 lines)
- Page Up/Down keys scroll by page size
- Scroll indicators show lines above/below: ─── ↑ 5 more ───

Breaking change: Editor constructor signature changed from
  new Editor(theme)
to
  new Editor(tui, theme)

fixes #732

packages/tui/README.md

@@ -27,7 +27,7 @@ const tui = new TUI(terminal);
 // Add components
 tui.addChild(new Text("Welcome to my app!"));
 
-const editor = new Editor(editorTheme);
+const editor = new Editor(tui, editorTheme);
 editor.onSubmit = (text) => {
   console.log("Submitted:", text);
   tui.addChild(new Text(`You said: ${text}`));
@@ -212,7 +212,7 @@ input.getValue();
 
 ### Editor
 
-Multi-line text editor with autocomplete, file completion, and paste handling.
+Multi-line text editor with autocomplete, file completion, paste handling, and vertical scrolling when content exceeds terminal height.
 
 ```typescript
 interface EditorTheme {
@@ -220,7 +220,7 @@ interface EditorTheme {
   selectList: SelectListTheme;
 }
 
-const editor = new Editor(theme);
+const editor = new Editor(tui, theme);  // tui is required for height-aware scrolling
 editor.onSubmit = (text) => console.log(text);
 editor.onChange = (text) => console.log("Changed:", text);
 editor.disableSubmit = true; // Disable submit temporarily