The design's split.jsx Pane header leads with an 8 px brand-accent dot,
the lock indicator, host name in INK, then the tab title in INK_4.
The previous header rendered a 24 px brand glyph plus the URL path —
visually heavier and less informative once both panes share most of
their URL prefix.
* brand_glyph: `brand_accent_color(brand)` and `accent_color_for_host`
collapse each Brand to one design-matching dot color (Figma 7c6cf7,
Linear 5e6ad2, etc.).
* split_pane: 32 → 30 px header, glyph → 8 px dot, URL path → tab
title in INK_4. `pane_path_label` deleted; nothing else used it.
cargo test --workspace: 440 passed, 0 failed.
ZacharyZhang-NY
cbcc45bd7b