Theme navigation icons

Purpose: Give the Word97, Chicago and Midnight themes a 16px pixel-art glyph on each navigation destination without changing markup or server HTML. Scenario: A reader in one of those themes sees a glyph before the label of every main navigation link, Tools bar link, Tools launcher button, Bookmarklets button and launcher group heading. The glyph is chosen in CSS from the link's href (board filters use data-nav-key, bookmarklets data-bookmarklet-kind, launcher group headings data-shape), so adding or renaming a destination means adding or moving one rule keyed to its link, for both the launcher button and the Tools bar link where the destination is a tool. Every other theme shows the same markup as text only. The theme menu never receives icons. Sources: icon stylesheet (source unavailable) (the :root:is(...) theme list at the top adds a theme to the set), the rule to keep icons current, launcher matrix test (source unavailable) (asserts a non-empty glyph on each tool button, bar link and group heading in the three themes).

Group heading glyphs: a monitor (device), an open book (reading), the Users glyph (community) and a gear drawn mid-grey with a white ring so it reads on light and dark panels (operator). Account's Tools bar rule remains in the stylesheet although Account is no longer a tool; its main navigation rule still applies.

Tool glyphs added later keep the same 16px grid; Deploy (an arrow rising out of a tray) follows Operations in the operator group.