Light mode: add missing --accent-green-border and --shadow-color tokens

The light theme defined --accent-cyan-border but not --accent-green-border, so
consumers using the green border token fell back to the dark theme's neon value
in light mode. There was also no shadow token at all, leaving apps to hardcode
rgba(0,0,0,0.5) — far too heavy on light surfaces.

Adds --accent-green-border and --shadow-color to both themes.

base.css

@@ -66,6 +66,7 @@
   --accent-green-bright: #33FFAA;
   --accent-green-dim:    rgba(0,255,136,0.10);
   --accent-green-border: rgba(0,255,136,0.22);
+  --shadow-color:        rgba(0,0,0,0.5);
 
   /* --- Error / Critical --- */
   --accent-red:     #FF2D55;
@@ -3648,6 +3649,8 @@ html[data-theme="light"] {
   --accent-red-dim:      rgba(181,0,31,0.10);
   --accent-amber-dim:    rgba(138,90,0,0.10);
   --accent-cyan-border:  rgba(0,98,184,0.28);
+  --accent-green-border: rgba(0,109,53,0.28);
+  --shadow-color:        rgba(50,80,130,0.18);
 
   /* — Glows become subtle drop shadows in light mode — */
   --glow-orange:         0 0 0 1px rgba(196,78,0,0.25),  0 1px 6px rgba(196,78,0,0.18);