feat: migrar dashboard a React 19 + TypeScript + Vite + Tailwind v4

- Módulo HITL (/cases): 6 patrones de formularios dinámicos para 53 tipos de caso con validación Zod
- Módulo Monitor (/monitor): streaming token-a-token en tiempo real, auto-scroll y notas internas vía WebSocket
- Arquitectura híbrida: REST (canal autoritativo) + WebSocket (difusión/streaming)
- MSW para desarrollo sin backend, hooks de notificaciones/sonido/título preservados
- Backend legacy movido a legacy/, archivos residuales eliminados de raíz

src/hooks/useSound.ts

@@ -0,0 +1,114 @@
+import { useRef, useEffect, useCallback } from 'react';
+
+// ─────────────────────────────────────────────────────────────
+// Constants
+// ─────────────────────────────────────────────────────────────
+
+/** C5 frequency in Hz (523.25) */
+const C5 = 523.25;
+
+/** E5 frequency in Hz (659.25) */
+const E5 = 659.25;
+
+/** Duration of each tone in seconds (120 ms) */
+const TONE_DURATION = 0.12;
+
+/** Overall gain / volume (0.08 = 8%) */
+const VOLUME = 0.08;
+
+/** Exponential fade-out duration in seconds (450 ms) */
+const FADE_DURATION = 0.45;
+
+// ─────────────────────────────────────────────────────────────
+// useSound
+// ─────────────────────────────────────────────────────────────
+
+/**
+ * Hook for playing a notification chime using the Web Audio API.
+ *
+ * - Initialises an `AudioContext` lazily on the first user gesture
+ *   (click or keydown) to comply with browser autoplay policies.
+ * - Exposes `playNotificationSound()` which plays a two‑tone chime:
+ *   C5 (523.25 Hz) for 120 ms → E5 (659.25 Hz) for 120 ms,
+ *   with a shared exponential fade‑out envelope (0.08 → 0.001 over 450 ms).
+ * - If the `AudioContext` is suspended, a warning is logged and the
+ *   call is silently ignored.
+ */
+export function useSound() {
+  const audioCtxRef = useRef<AudioContext | null>(null);
+  const initializedRef = useRef(false);
+
+  // ── Lazy initialisation on first user gesture ──────────────
+  useEffect(() => {
+    const initAudio = () => {
+      if (initializedRef.current) return;
+
+      try {
+        audioCtxRef.current = new AudioContext();
+        initializedRef.current = true;
+      } catch (err) {
+        console.warn('[useSound] Web Audio API is not available:', err);
+      }
+
+      // Remove both listeners after the first gesture
+      window.removeEventListener('click', initAudio);
+      window.removeEventListener('keydown', initAudio);
+    };
+
+    // Attach listeners for first gesture
+    window.addEventListener('click', initAudio, { once: true });
+    window.addEventListener('keydown', initAudio, { once: true });
+
+    return () => {
+      window.removeEventListener('click', initAudio);
+      window.removeEventListener('keydown', initAudio);
+
+      // Close AudioContext on unmount
+      const ctx = audioCtxRef.current;
+      if (ctx) {
+        ctx.close().catch(() => {});
+        audioCtxRef.current = null;
+      }
+      initializedRef.current = false;
+    };
+  }, []);
+
+  // ── Play the two‑tone chime ────────────────────────────────
+  const playNotificationSound = useCallback((): void => {
+    const ctx = audioCtxRef.current;
+
+    if (!ctx) {
+      console.warn('[useSound] AudioContext has not been initialised yet');
+      return;
+    }
+
+    if (ctx.state === 'suspended') {
+      console.warn('[useSound] AudioContext is suspended — cannot play sound');
+      return;
+    }
+
+    const now = ctx.currentTime;
+
+    // Single shared gain node for both oscillators → unified fade‑out
+    const gain = ctx.createGain();
+    gain.gain.setValueAtTime(VOLUME, now);
+    gain.gain.exponentialRampToValueAtTime(0.001, now + FADE_DURATION);
+    gain.connect(ctx.destination);
+
+    // Helper: create and schedule a single sine‑wave tone
+    const playTone = (frequency: number, startTime: number): void => {
+      const osc = ctx.createOscillator();
+      osc.type = 'sine';
+      osc.frequency.setValueAtTime(frequency, startTime);
+      osc.connect(gain);
+      osc.start(startTime);
+      osc.stop(startTime + TONE_DURATION);
+    };
+
+    // Schedule the two tones
+    playTone(C5, now);       // C5 starts immediately
+    playTone(E5, now + TONE_DURATION); // E5 starts after C5 ends
+  }, []);
+
+  return { playNotificationSound };
+}