Statusbar badge symbols should use the symbols map

[erikjuhani]

The statusbar renders powerline-style glyphs (U+E0B6 and U+E0B4) as left/right badge corners around the active component name. These are hardcoded in statusbar.rs and not part of the Symbols struct, so they render as tofu in ASCII mode.

Problem

basalt/src/statusbar.rs:42-49 — the badge is built with literal powerline chars:

let active_component = [
    Span::from("").dark_gray(),       // U+E0B6
    Span::from(" ").bg(Color::DarkGray),
    Span::from(state.active_component_name)...,
    Span::from(" ").bg(Color::DarkGray),
    Span::from("").dark_gray(),       // U+E0B4
];

These are Private Use Area codepoints from the powerline/nerd font range. They only render in terminals with a patched font. On the ASCII preset they show as replacement characters.

The StatusBar widget currently takes no reference to Config or Symbols — it is constructed via StatusBar::default() and rendered without symbol access (basalt/src/app.rs:638).

Design

Add two new fields to Symbols:

Field	ASCII	Unicode / NerdFont
statusbar_badge_left		`` (U+E0B6)
statusbar_badge_right		`` (U+E0B4)

Thread &Symbols (or just the two strings) into StatusBar so it can use them instead of hardcoded literals.

The ASCII fallback uses whitespace string, which pair naturally with the reversed-color background that's already applied to give space.

Pseudo code

// config/symbol.rs — add to Symbols struct
pub statusbar_badge_left: String,
pub statusbar_badge_right: String,

// ascii()
statusbar_badge_left: " ".into(),
statusbar_badge_right: " ".into(),

// unicode() and nerd_font()
statusbar_badge_left: "\u{e0b6}".into(),
statusbar_badge_right: "\u{e0b4}".into(),

Also add corresponding Option<String> fields to TomlSymbols and entries in the override_if_set! macro so users can customize them.