Function render_inline_editor 

pub fn render_inline_editor(
    frame: &mut Frame<'_>,
    area: Rect,
    editor: &InlineEditor,
    theme: &Theme,
)

Render the inline editor into the given area.

Layout (top to bottom):

1. Header — 1 line: ✏️ Editing: <filename> [modified]
2. Content — remaining lines minus footer: line numbers + text
3. Footer — 1 line: status message + cursor position + key hints