feat: Complete light mode implementation with semantic theme system (#450)

- Add comprehensive light/dark mode CSS variables with semantic naming
- Implement theme-aware scrollbars using CSS variables
- Add light mode backgrounds: --bg-base, --bg-elevated, --bg-surface, etc.
- Add theme-aware borders: --border-base, --border-panel, --border-subtle
- Add semantic text colors: --foreground-secondary, --foreground-subtle
- Convert oklch colors to hex for better compatibility
- Add theme awareness to CodeMirror editors
- Update dark mode colors for consistency (background, sidebar, card, muted, input)
- Add Tailwind color mappings for semantic classes

Co-authored-by: Luke Gustafson <88517757+LukeGus@users.noreply.github.com>

src/main.tsx

@@ -79,13 +79,13 @@ function RootApp() {
       <div
         className="fixed inset-0 pointer-events-none"
         style={{
-          backgroundColor: "#09090b",
+          backgroundColor: "var(--bg-base)",
           backgroundImage: `linear-gradient(
             135deg,
             transparent 0%,
             transparent 49%,
-            rgba(255, 255, 255, 0.03) 49%,
-            rgba(255, 255, 255, 0.03) 51%,
+            rgba(128, 128, 128, 0.03) 49%,
+            rgba(128, 128, 128, 0.03) 51%,
             transparent 51%,
             transparent 100%
           )`,