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/.env.example

@@ -0,0 +1,18 @@
+# Grafana Faro (browser RUM) — Vite build-time env vars.
+# These are inlined into the production bundle at build time.
+# Copy to .env and adjust as needed for local dev.
+
+# OTLP HTTP endpoint of the Grafana Alloy collector.
+# In Docker on the same host as Alloy, use http://localhost:4318 (the
+# container's perspective of the host). For external deploys, use the
+# Alloy's public URL, e.g. https://alloy.example.com.
+VITE_FARO_ENDPOINT=http://localhost:4318
+
+# App name shown in Grafana Explore / Faro data source.
+VITE_FARO_APP_NAME=farmafinder-frontend
+
+# Environment label (production | staging | development).
+VITE_FARO_ENV=production
+
+# App version (set by CI from the package version or git tag).
+VITE_FARO_APP_VERSION=1.0.0