refactor: unify docker deployment and restructure frontend architecture

This commit implements a unified Docker deployment strategy, moving from separate frontend and backend images to a single, multi-stage build image containing both services. It also introduces a major reorganization of the frontend directory structure and simplifies the environment configuration.

Key changes:
- **Deployment**: Added a multi-stage `Dockerfile` and `docker-entrypoint.sh` to package the Go backend and Nginx-served frontend into a single container.
- **CI/CD**: Updated GitHub Actions workflows (`ci-cd.yml`, `release.yml`) to build and push the new unified image instead of separate ones.
- **Frontend Refactor**: Reorganized `frontend/src/pages` into a domain-driven directory structure (e.g., `auth/`, `admin/`, `content/`, `communication/`, `productivity/`, `settings/`, `misc/`).
- **Configuration**: Simplified `.env.example` and updated `docker-compose.yml` to reflect the unified service model and single host port.
- **Cleanup**: Removed deprecated `docker-compose.demo.yml`, `docker-compose.prod.yml`, and various unused frontend components and services.
- **Backend**: Refactored configuration loading to use exported `GetDurationEnv` for better consistency.

Dockerfile

@@ -0,0 +1,55 @@
+# Multi-stage build for unified Trackeep image
+# Builds both frontend and backend in one package
+
+# Stage 1: Build Frontend
+FROM node:22-alpine AS frontend-builder
+WORKDIR /app/frontend
+COPY frontend/package*.json ./
+RUN npm ci --only=production
+COPY frontend/ ./
+RUN npm run build
+
+# Stage 2: Build Backend
+FROM golang:1.25-alpine AS backend-builder
+WORKDIR /app/backend
+COPY backend/go.mod backend/go.sum ./
+RUN go mod download
+COPY backend/ ./
+RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o main .
+
+# Stage 3: Final unified image
+FROM alpine:latest
+
+# Install dependencies
+RUN apk --no-cache add ca-certificates tzdata nginx
+
+# Copy backend binary and migrations
+COPY --from=backend-builder /app/backend/main /app/main
+COPY --from=backend-builder /app/backend/migrations /app/migrations
+
+# Copy frontend build
+COPY --from=frontend-builder /app/frontend/dist /usr/share/nginx/html
+
+# Copy branding assets
+COPY trackeep.svg /usr/share/nginx/html/
+COPY trackeepfavi.png /usr/share/nginx/html/
+COPY trackeepfavi_bg.png /usr/share/nginx/html/
+
+# Copy nginx configuration
+COPY frontend/nginx.conf /etc/nginx/nginx.conf
+
+# Create directories
+RUN mkdir -p /app/uploads /data /var/log/nginx
+
+# Expose single port
+EXPOSE 8080
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD wget --no-verbose --tries=1 --spider http://localhost:8080/health || exit 1
+
+# Start script to run both backend and nginx
+COPY docker-entrypoint.sh /docker-entrypoint.sh
+RUN chmod +x /docker-entrypoint.sh
+
+ENTRYPOINT ["/docker-entrypoint.sh"]