Replace the colored accent dot in each split pane header with the
host's brand glyph, and add the design's reload control next to the
close glyph. The header height bumps from 30 to 32 px so the 16 px
glyph sits cleanly between the 11 px lock and host text.
splits.rs had grown to 551 lines after adding the design's pane header.
Move the header renderer, the close glyph, the URL helpers, and the
compact-canvas placeholder into chrome::split_pane so splits.rs is back
to a 422-line action + render orchestrator and the new helpers stay
under their own 150-line file.
Behaviour preserved: the pane click still selects the tab, the close
glyph still selects+closes, and pane_host/path/secure still derive from
the same UrlText fields.
ZacharyZhang-NY