fix(glass): soften the Matrix scheme accent (neon phosphor → muted emerald)

UAT: #2fe36e read as too vivid/stabby. Drop to #46b87c (lower saturation) +
slightly less green-tinted fg; update the swatch to match.

frontend/src/index.css

@@ -318,16 +318,16 @@ html[data-scheme="starship"][data-theme="light"] {
   --accent-fg: #ffffff;
 }
 
-/* Matrix — near-black with a phosphor-green terminal accent */
+/* Matrix — near-black with a muted terminal-green accent (softened from neon phosphor) */
 html[data-scheme="matrix"][data-theme="dark"] {
   --bg: #030a06;
   --surface: #08130d;
   --card: #0b1c12;
   --border: #163d27;
-  --fg: #d6ffe4;
+  --fg: #cfe8d6;
   --muted: #6fae86;
-  --accent: #2fe36e;
-  --accent-fg: #02160a;
+  --accent: #46b87c;
+  --accent-fg: #04170c;
 }
 html[data-scheme="matrix"][data-theme="light"] {
   --bg: #f0f7f1;

frontend/src/lib/theme.ts

@@ -9,7 +9,7 @@ export const SCHEMES: { id: Scheme; name: string; swatch: string }[] = [
   { id: "slate", name: "Slate", swatch: "#e8913c" },
   { id: "youtube", name: "YouTube", swatch: "#ff3b46" },
   { id: "starship", name: "Starship", swatch: "#38b6ff" },
-  { id: "matrix", name: "Matrix", swatch: "#2fe36e" },
+  { id: "matrix", name: "Matrix", swatch: "#46b87c" },
 ];
 
 export interface ThemePrefs {