feat(i18n): add internationalization with DE, FR, ES, PT translations

Add a compile-time i18n system with 270 translation keys across 5 locales
(EN, DE, FR, ES, PT). Translations are embedded via include_str! and parsed
lazily into flat HashMaps with English fallback for missing keys.

- Add src/i18n module with Locale enum, t()/tw() lookup functions, and tests
- Add JSON translation files for all 5 locales under assets/i18n/
- Provide locale Signal via Dioxus context in App, persisted to localStorage
- Replace all hardcoded UI strings across 33 component/page files
- Add compact locale picker (globe icon + ISO alpha-2 code) in sidebar header
- Add click-outside backdrop dismissal for locale dropdown

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/pages/dashboard.rs

@@ -2,6 +2,7 @@ use dioxus::prelude::*;
 use dioxus_sdk::storage::use_persistent;
 
 use crate::components::{ArticleDetail, DashboardSidebar, NewsCardView, PageHeader};
+use crate::i18n::{t, Locale};
 use crate::infrastructure::chat::{create_chat_session, save_chat_message};
 use crate::infrastructure::llm::FollowUpMessage;
 use crate::models::NewsCard;
@@ -28,6 +29,9 @@ const DEFAULT_TOPICS: &[&str] = &[
 /// - `certifai_ollama_model`: Ollama model ID for summarization
 #[component]
 pub fn DashboardPage() -> Element {
+    let locale = use_context::<Signal<Locale>>();
+    let l = *locale.read();
+
     // Persistent state stored in localStorage
     let mut custom_topics = use_persistent("certifai_topics".to_string(), Vec::<String>::new);
     // Default to empty so the server functions use OLLAMA_URL / OLLAMA_MODEL
@@ -133,8 +137,8 @@ pub fn DashboardPage() -> Element {
     rsx! {
         section { class: "dashboard-page",
             PageHeader {
-                title: "Dashboard".to_string(),
-                subtitle: "AI news and updates".to_string(),
+                title: t(l, "dashboard.title"),
+                subtitle: t(l, "dashboard.subtitle"),
             }
 
             // Topic tabs row
@@ -188,7 +192,7 @@ pub fn DashboardPage() -> Element {
                         input {
                             class: "topic-input",
                             r#type: "text",
-                            placeholder: "Topic name...",
+                            placeholder: "{t(l, \"dashboard.topic_placeholder\")}",
                             value: "{new_topic_text}",
                             oninput: move |e| new_topic_text.set(e.value()),
                             onkeypress: move |e| {
@@ -214,7 +218,7 @@ pub fn DashboardPage() -> Element {
                                 show_add_input.set(false);
                                 new_topic_text.set(String::new());
                             },
-                            "Cancel"
+                            "{t(l, \"common.cancel\")}"
                         }
                     }
                 } else {
@@ -236,33 +240,33 @@ pub fn DashboardPage() -> Element {
                         }
                         show_settings.set(!currently_shown);
                     },
-                    "Settings"
+                    "{t(l, \"common.settings\")}"
                 }
             }
 
             // Settings panel (collapsible)
             if *show_settings.read() {
                 div { class: "settings-panel",
-                    h4 { class: "settings-panel-title", "Ollama Settings" }
+                    h4 { class: "settings-panel-title", "{t(l, \"dashboard.ollama_settings\")}" }
                     p { class: "settings-hint",
-                        "Leave empty to use OLLAMA_URL / OLLAMA_MODEL from .env"
+                        "{t(l, \"dashboard.settings_hint\")}"
                     }
                     div { class: "settings-field",
-                        label { "Ollama URL" }
+                        label { "{t(l, \"dashboard.ollama_url\")}" }
                         input {
                             class: "settings-input",
                             r#type: "text",
-                            placeholder: "Uses OLLAMA_URL from .env",
+                            placeholder: "{t(l, \"dashboard.ollama_url_placeholder\")}",
                             value: "{settings_url}",
                             oninput: move |e| settings_url.set(e.value()),
                         }
                     }
                     div { class: "settings-field",
-                        label { "Model" }
+                        label { "{t(l, \"dashboard.model\")}" }
                         input {
                             class: "settings-input",
                             r#type: "text",
-                            placeholder: "Uses OLLAMA_MODEL from .env",
+                            placeholder: "{t(l, \"dashboard.model_placeholder\")}",
                             value: "{settings_model}",
                             oninput: move |e| settings_model.set(e.value()),
                         }
@@ -274,14 +278,14 @@ pub fn DashboardPage() -> Element {
                             *ollama_model.write() = settings_model.read().trim().to_string();
                             show_settings.set(false);
                         },
-                        "Save"
+                        "{t(l, \"common.save\")}"
                     }
                 }
             }
 
             // Loading / error state
             if is_loading {
-                div { class: "dashboard-loading", "Searching..." }
+                div { class: "dashboard-loading", "{t(l, \"dashboard.searching\")}" }
             }
             if let Some(ref err) = search_error {
                 div { class: "settings-hint", "{err}" }