feat(fullstack): implement observability and redesign frontend UI

This commit introduces comprehensive observability for both backend and frontend, alongside a major UI/UX overhaul to align with modern design standards (Material 3 inspired) and improve localization.

Backend changes:
- Integrated OpenTelemetry SDK for distributed tracing.
- Added Pino for structured JSON logging with OTel instrumentation for trace/span correlation.
- Configured OTLP exporters to route traces and logs to Grafana Alloy.
- Updated docker-compose to include necessary environment variables for observability.

Frontend changes:
- Integrated Grafana Faro for Real User Monitoring (RUM), capturing Web Vitals, JS errors, and user interactions.
- Redesigned the entire UI using a new color palette and Material 3 design principles.
- Refactored component architecture (App, Home, Search, Scanner, Profile, Alerts views) for better state management and navigation.
- Improved mobile UX with a redesigned Bottom Navigation bar and Top Bar.
- Localized the interface to Spanish (es).
- Updated assets, icons, and PWA configuration (manifest, icons).
- Refactored CSS to use a centralized design token system (CSS variables).

Observability enables better debugging and performance monitoring across the entire stack.

frontend/src/components/BottomNav.css

@@ -1,23 +1,22 @@
-/* BottomNav — mobile-only fixed bottom tab bar. Desktop hides via display:none above 768px. */
-
 .bottom-nav {
   display: none;
 }
 
 @media (max-width: 768px) {
   .bottom-nav {
-    display: grid;
-    grid-template-columns: repeat(4, 1fr);
+    display: flex;
+    justify-content: space-around;
+    align-items: flex-end;
     position: fixed;
     left: 0;
     right: 0;
     bottom: 0;
     z-index: 50;
-    padding: 0.4rem 0.5rem calc(0.4rem + env(safe-area-inset-bottom));
-    background: var(--glass-bg);
-    -webkit-backdrop-filter: saturate(180%) blur(20px);
-    backdrop-filter: saturate(180%) blur(20px);
-    border-top: 1px solid var(--border);
+    padding: 0.25rem 0.5rem calc(0.5rem + env(safe-area-inset-bottom));
+    background: var(--surface-container-lowest);
+    box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.1);
+    border-radius: var(--radius-lg) var(--radius-lg) 0 0;
+    height: 5.5rem;
   }
 
   .bottom-nav-item {
@@ -25,19 +24,21 @@
     flex-direction: column;
     align-items: center;
     justify-content: flex-end;
-    gap: 0.25rem;
-    padding: 0.25rem 0.25rem 0.1rem;
+    gap: 0.15rem;
+    padding: 0.25rem 0.5rem;
     background: transparent;
     border: none;
     cursor: pointer;
-    color: var(--text-muted);
+    color: var(--on-surface-variant);
     font: inherit;
     -webkit-tap-highlight-color: transparent;
     transition: color 0.15s;
+    position: relative;
+    min-width: 3.5rem;
   }
 
   .bottom-nav-item.disabled {
-    opacity: 0.5;
+    opacity: 0.4;
     cursor: not-allowed;
   }
 
@@ -45,45 +46,78 @@
     display: inline-flex;
     align-items: center;
     justify-content: center;
-    width: 2.5rem;
-    height: 2.5rem;
-    border-radius: 999px;
+    width: 2.75rem;
+    height: 2.75rem;
+    border-radius: var(--radius-full);
     color: inherit;
-    transition: background 0.2s, color 0.2s, transform 0.2s;
+    position: relative;
   }
 
-  /* Elevated center tab (Scan) — sits above the bar like iOS center FAB */
-  .bottom-nav-item:nth-child(2) {
-    margin-top: -1.1rem;
+  .nav-fab {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    width: 3.5rem;
+    height: 3.5rem;
+    border-radius: var(--radius-full);
+    background: var(--tertiary-container);
+    color: var(--on-tertiary);
+    box-shadow: 0 4px 14px rgba(70, 0, 173, 0.35);
+    margin-top: -1.5rem;
+    transition: transform 0.15s;
   }
 
-  .nav-icon-wrap--elevated {
-    background: var(--primary);
-    color: #fff;
-    width: 3.25rem;
-    height: 3.25rem;
-    box-shadow:
-      0 0 0 4px var(--glass-bg),
-      0 8px 18px rgba(15, 118, 110, 0.4),
-      0 2px 6px rgba(15, 118, 110, 0.25);
+  .nav-fab:active {
+    transform: scale(0.92);
   }
 
-  .bottom-nav-item.active .nav-label {
+  .nav-badge {
+    position: absolute;
+    top: 0;
+    right: -2px;
+    width: 1.125rem;
+    height: 1.125rem;
+    background: var(--error);
+    color: var(--on-error);
+    font-size: 0.625rem;
+    font-weight: 700;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border-radius: var(--radius-full);
+    border: 2px solid var(--surface-container-lowest);
+    line-height: 1;
+  }
+
+  .nav-label {
+    font-size: 0.7rem;
+    font-weight: 500;
+    line-height: 1;
+    color: var(--on-surface-variant);
+  }
+
+  .nav-label--active {
     color: var(--primary);
     font-weight: 700;
   }
 
-  .bottom-nav-item.active .nav-icon-wrap:not(.nav-icon-wrap--elevated) {
+  .nav-indicator {
+    width: 0.375rem;
+    height: 0.375rem;
+    background: var(--primary);
+    border-radius: var(--radius-full);
+    margin-top: 0.125rem;
+  }
+
+  .bottom-nav-item.active .nav-icon-wrap {
     color: var(--primary);
   }
 
-  .bottom-nav-item:active .nav-icon-wrap--elevated {
-    transform: scale(0.94);
+  .bottom-nav-item.active .nav-icon-wrap svg {
+    stroke-width: 2.5;
   }
 
-  .nav-label {
-    font-size: 0.68rem;
-    line-height: 1;
-    letter-spacing: 0.01em;
+  .nav-elevated.active .nav-label {
+    color: var(--tertiary);
   }
-}
+}