docs site: gentler colours from the co-op design system, dark mode off Material slate

Light: warm neutrals (#e4e0d8 borders, #f4f2ec code, #6b7a62 muted) instead of
near-blacks; links use the dashboard's #4e7a4d (4.7:1 on cream).

Dark: replace Material's cold blue-grey slate (#1e2129 page) with the chat
overlay's deep-pine palette (#22271f page, #e8f5e8 text, #7ab87a accent), so a
dark screen reads as the co-op's green identity rather than stock Material.

publishing/typography.css

@@ -58,10 +58,19 @@ body,
 /* Long prose stays readable; measured in characters rather than pixels. */
 .md-typeset { line-height: 1.65; }
 
-/* Colour is scheme-specific, so it stays out of the rules above. */
+/* Colour is scheme-specific, so it stays out of the rules above.
+ * Light: the co-op's warm ink (#2d3327), never a neutral near-black.
+ * Dark: the chat overlay's light warm text (#e8f5e8) on the deep-pine page. */
 [data-md-color-scheme="default"] .md-typeset h1,
 [data-md-color-scheme="default"] .md-typeset h2,
 [data-md-color-scheme="default"] .md-typeset h3,
 [data-md-color-scheme="default"] .md-typeset h4 {
   color: #2d3327;
 }
+
+[data-md-color-scheme="slate"] .md-typeset h1,
+[data-md-color-scheme="slate"] .md-typeset h2,
+[data-md-color-scheme="slate"] .md-typeset h3,
+[data-md-color-scheme="slate"] .md-typeset h4 {
+  color: #e8f5e8;
+}