Add DE/EN language toggle with bilingual descriptions

- Language switcher in sidebar (DE/EN buttons, persists to localStorage)
- i18n module with pick_desc/pick_name helpers for language-aware fallback
- All detail/list pages use language context for names and descriptions
- Species/Cultivar types updated with description_de/description_en
- Common Name column added to species/families lists

herbapi-ui/src/pages/home.rs

@@ -1,11 +1,13 @@
 use dioxus::prelude::*;
 
 use crate::api;
-use crate::app::Route;
+use crate::app::{Lang, Route};
 use crate::components::plant_card::PlantCard;
+use crate::i18n::pick_name;
 
 #[component]
 pub fn Home() -> Element {
+    let lang = use_context::<Lang>().0;
     let mut search_query = use_signal(|| String::new());
     let species = use_resource(|| async { api::list_species(1, 12, None, None).await });
 
@@ -36,12 +38,18 @@ pub fn Home() -> Element {
                 Some(Ok(data)) => rsx! {
                     div { class: "card-grid",
                         for s in data.data.iter().take(12) {
-                            PlantCard {
-                                key: "{s.id}",
-                                slug: s.slug.clone(),
-                                name: s.name_scientific.clone(),
-                                name_common: s.name_en.clone(),
-                                entity_type: "species".to_string(),
+                            {
+                                let card_common = pick_name(&lang.read(), &s.name_de, &s.name_en, &s.name_scientific);
+                                let show_common = if card_common == s.name_scientific { None } else { Some(card_common) };
+                                rsx! {
+                                    PlantCard {
+                                        key: "{s.id}",
+                                        slug: s.slug.clone(),
+                                        name: s.name_scientific.clone(),
+                                        name_common: show_common,
+                                        entity_type: "species".to_string(),
+                                    }
+                                }
                             }
                         }
                     }