feat(web): add theme definition system with 5 built-in themes (#493)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/web/src/themes/solarized-dark.ts

@@ -0,0 +1,45 @@
+import type { ThemeDefinition } from "./types";
+
+/**
+ * Solarized Dark theme — precision colors for machines and people.
+ * Based on https://ethanschoonover.com/solarized/
+ */
+export const solarizedDarkTheme: ThemeDefinition = {
+  id: "solarized-dark",
+  name: "Solarized Dark",
+  description: "Precision color palette with selective contrast relationships",
+  author: "Ethan Schoonover",
+  isDark: true,
+  colorPreview: ["#002b36", "#073642", "#fdf6e3", "#268bd2", "#6c71c4"],
+  colors: {
+    "bg-950": "#001e26",
+    "bg-900": "#002b36",
+    "bg-850": "#04313d",
+    "surface-800": "#073642",
+    "surface-750": "#174452",
+    "border-700": "#2a5565",
+    "text-100": "#fdf6e3",
+    "text-300": "#93a1a1",
+    "text-500": "#657b83",
+    "blue-500": "#268bd2",
+    "blue-400": "#4ba2de",
+    "red-500": "#dc322f",
+    "red-400": "#e35855",
+    "purple-500": "#6c71c4",
+    "purple-400": "#8b8fd3",
+    "teal-500": "#2aa198",
+    "teal-400": "#47b5ad",
+    "amber-500": "#b58900",
+    "amber-400": "#cba020",
+    "pink-500": "#d33682",
+    "emerald-500": "#859900",
+    "orange-500": "#cb4b16",
+    "cyan-500": "#36bcb3",
+    "indigo-500": "#4b66c4",
+  },
+  shadows: {
+    sm: "0 1px 2px 0 rgb(0 0 0 / 0.35)",
+    md: "0 4px 6px -1px rgb(0 0 0 / 0.45), 0 2px 4px -2px rgb(0 0 0 / 0.35)",
+    lg: "0 10px 15px -3px rgb(0 0 0 / 0.55), 0 4px 6px -4px rgb(0 0 0 / 0.45)",
+  },
+};