Initial commit: React frontend (SLP Software) + AIDLC workflow docs

Co-authored-by: Junie <junie@jetbrains.com>

src/theme/ThemeProvider.tsx

@@ -0,0 +1,65 @@
+import { createContext, useCallback, useContext, useEffect, useMemo, useState } from 'react';
+import type { ReactNode } from 'react';
+import {
+  DEFAULT_THEME,
+  THEME_STORAGE_KEY,
+  resolveInitialTheme,
+  themeClassName,
+  type ThemeName,
+} from './tokens';
+
+interface ThemeContextValue {
+  theme: ThemeName;
+  toggleTheme: () => void;
+}
+
+const ThemeContext = createContext<ThemeContextValue | undefined>(undefined);
+
+function readStoredTheme(): string | null {
+  try {
+    return window.localStorage.getItem(THEME_STORAGE_KEY);
+  } catch {
+    // BR-3: treat unavailable/unreadable storage the same as "nothing stored" — fall back to default.
+    return null;
+  }
+}
+
+function persistTheme(theme: ThemeName): void {
+  try {
+    window.localStorage.setItem(THEME_STORAGE_KEY, theme);
+  } catch {
+    // Ignore write failures (e.g. storage disabled) — theme still works for this session via state.
+  }
+}
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  const [theme, setTheme] = useState<ThemeName>(() => resolveInitialTheme(readStoredTheme()));
+
+  useEffect(() => {
+    const root = document.documentElement;
+    root.classList.remove('theme-red', 'theme-purple');
+    root.classList.add(themeClassName(theme));
+  }, [theme]);
+
+  const toggleTheme = useCallback(() => {
+    setTheme((current) => {
+      const next: ThemeName = current === 'red' ? 'purple' : 'red';
+      persistTheme(next);
+      return next;
+    });
+  }, []);
+
+  const value = useMemo<ThemeContextValue>(() => ({ theme, toggleTheme }), [theme, toggleTheme]);
+
+  return <ThemeContext.Provider value={value}>{children}</ThemeContext.Provider>;
+}
+
+export function useTheme(): ThemeContextValue {
+  const context = useContext(ThemeContext);
+  if (!context) {
+    throw new Error('useTheme must be used within a ThemeProvider');
+  }
+  return context;
+}
+
+export { DEFAULT_THEME };