fix: add missing brand-950 to Tailwind config

Root cause: brand-950 was used in 13+ files but never defined in
tailwind.config.ts (brand colors only went 50-900). All dark:bg-brand-950
classes produced no CSS output, making dark backgrounds invisible.

Fix: add brand-950 mapped to --accent-900 CSS variable (same as 900,
the darkest shade available). This makes all existing brand-950 classes
work across the entire codebase.

Co-Authored-By: claude-flow <ruv@ruv.net>

apps/web/tailwind.config.ts

@@ -17,6 +17,7 @@ const config: Config = {
           700: "rgb(var(--accent-700) / <alpha-value>)",
           800: "rgb(var(--accent-800) / <alpha-value>)",
           900: "rgb(var(--accent-900) / <alpha-value>)",
+          950: "rgb(var(--accent-900) / <alpha-value>)",
         },
       },
       fontFamily: {