Add data export functionality with gzip compression

- Add FindByUserID method to HabitEntryRepository (JOIN with habits)
- Implement ExportUserDataHandler to export all user data
- Add GET /api/v1/export endpoint with gzip compression
- Apply strict rate limiting (1 export per hour per user)
- Export includes all habits (active + archived) and entries
- Add i18n translations for export errors (en/es)
- Update all test mocks to implement new repository method
- Export format: JSON with gzip (~10x compression ratio)

internal/infrastructure/http/export_handlers.go

@@ -0,0 +1,65 @@
+package http
+
+import (
+	"compress/gzip"
+	"encoding/json"
+	"net/http"
+
+	"apocapoc-api/internal/application/queries"
+	"apocapoc-api/internal/i18n"
+)
+
+type ExportHandlers struct {
+	exportHandler *queries.ExportUserDataHandler
+	translator    *i18n.Translator
+}
+
+func NewExportHandlers(
+	exportHandler *queries.ExportUserDataHandler,
+	translator *i18n.Translator,
+) *ExportHandlers {
+	return &ExportHandlers{
+		exportHandler: exportHandler,
+		translator:    translator,
+	}
+}
+
+// ExportData godoc
+// @Summary Export user data
+// @Description Export all user habits and entries in JSON format with gzip compression. Limited to 1 export per hour.
+// @Tags export
+// @Security BearerAuth
+// @Produce json
+// @Success 200 {object} queries.ExportUserDataResult "Compressed JSON export"
+// @Failure 401 {object} ErrorResponse "Unauthorized"
+// @Failure 429 {object} ErrorResponse "Rate limit exceeded"
+// @Failure 500 {object} ErrorResponse "Internal server error"
+// @Router /export [get]
+func (h *ExportHandlers) ExportData(w http.ResponseWriter, r *http.Request) {
+	userID := r.Context().Value("user_id").(string)
+
+	query := queries.ExportUserDataQuery{
+		UserID: userID,
+	}
+
+	result, err := h.exportHandler.Handle(r.Context(), query)
+	if err != nil {
+		respondErrorI18n(w, r, h.translator, http.StatusInternalServerError, "export_failed")
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Content-Encoding", "gzip")
+	w.Header().Set("Content-Disposition", "attachment; filename=\"apocapoc-export.json.gz\"")
+	w.WriteHeader(http.StatusOK)
+
+	gzipWriter := gzip.NewWriter(w)
+	defer gzipWriter.Close()
+
+	encoder := json.NewEncoder(gzipWriter)
+	encoder.SetIndent("", "  ")
+
+	if err := encoder.Encode(result); err != nil {
+		return
+	}
+}