style: the ribbon takes the logo's colours

--w-accent is the logo's slate instead of Word's blue (5.1:1 on the chrome,
carries white), and the clay marks the contextual tabs — the pair meets where
those sit beside the normal ones. Both defined once from favicon.svg; the
label tone is darkened, the clay itself only 3.3:1 on white.

docs/architecture/ribbon.md

@@ -22,17 +22,23 @@ chrome is mounted at a time, so the two sets never coexist.
 ## Palette
 
 Word's greys live in `--w-*` in `global.css` — its own token set, not the app's, so the two
-chromes can look nothing alike while sharing a theme. Accent `--w-accent: #185abd`; the tab's
+chromes can look nothing alike while sharing a theme. The accent is **not** Word's blue but the
+logo's slate, `--brand-slate` (`#4c6c8a`, 5.1:1 on the chrome and carries white); the tab's
 active underline is 2.5px **inset 13px from each side**, not a full-width border.
 
+The logo's other colour, `--brand-clay`, marks the **contextual tabs** — the ones that exist only
+for the selected object — as their 2px bar, over a `--w-contextual` label darkened to stay
+readable (the clay itself is 3.3:1 on white). Both brand tokens are defined once, from
+`favicon.svg`; the classic chrome's island hairline already gradients between the same pair.
+
 `.ribbon` remaps the app's own tokens onto that palette (`--color-surface`, `--color-primary`,
 `--toolbar-btn-size`, …). Custom properties inherit, so every reused picker — `ColorPicker`,
 `HistoryButton`, `TablePicker`, `TableStylePicker`, the border pickers — adopts the ribbon's look
 with no edit of its own, while the classic toolbar keeps the themed set.
 
-**Dark** flips only the colours — every metric holds, so it is the same ribbon. The values are
-Word's dark mode: Fluent's dark neutrals, chrome `#1f1f1f` on surface `#292929`, and the accent
-lightened to `#479ef5` because `#185abd` on a dark chrome is unreadable. AllBlack goes on to
+**Dark** flips only the colours — every metric holds, so it is the same ribbon. The neutrals are
+Word's dark mode: Fluent's dark neutrals, chrome `#1f1f1f` on surface `#292929`; both brand tones
+lighten (`#8fb3cd` / `#e2916f`), unreadable on a dark chrome otherwise. AllBlack goes on to
 Word's Black theme (`#0f0f0f`), since the app's AllBlack canvas is darker than its dark one.
 
 That lightened accent cannot also carry white text, so a **second** pair exists for the one place