Function progress_bar 

pub fn progress_bar(
    pct: i32,
    fill_color: &str,
    theme: &Theme,
    marker_pct: Option<i32>,
) -> String

Build a fixed-width progress bar in Pango markup.

• pct is clamped to 0..=100.
• fill_color colors the filled (█) cells; theme.bar_empty colors the empty (░) cells.
• If marker_pct is Some, a single █ in theme.marker color is placed at the corresponding cell, displacing one empty cell and (when usage exceeds the marker position) splitting the filled run around it.

Implementation note: this mirrors claudebar:225-250’s two-branch logic but in a single expression. The resulting markup is byte-identical for the same inputs.