Adds a Selection Marker toggle under Settings → Preferences that
controls the ❯ cursor glyph on the focused row of every list.
Default off; rows keep a leading space for alignment either way.
Every list pane (tab strip, feed, my shows, discover, search,
settings, whitelist editor) reads the glyph through the shared
useSelectionMarker hook.
Also aligns the lead column across panes: page list rows drop
their extra box paddingLeft so labels start at the same column
as the tab strip (2 cells without nerd icons, 4 with), keeping
episode sub-rows aligned to the title.
Tabs, Discover categories (replacing unused placeholder glyphs), Settings
sections, and the Feed 'Fetch More' row get Nerd Font glyphs (Font Awesome PUA
codepoints). When the terminal font isn't Nerd Font capable the glyphs render
nothing at all — no tofu, no layout gaps — via supportsNerdFonts() (env
allowlist + PODTUI_NERD_FONTS=1/0 override). Documented in README (Configuration
-> Fonts).
