feat(i18n): add internationalization with DE, FR, ES, PT translations (#12)

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>

Co-authored-by: Sharang Parnerkar <parnerkarsharang@gmail.com>
Reviewed-on: #12

src/components/article_detail.rs

@@ -1,6 +1,8 @@
+use dioxus::prelude::*;
+
+use crate::i18n::{t, Locale};
 use crate::infrastructure::llm::FollowUpMessage;
 use crate::models::NewsCard;
-use dioxus::prelude::*;
 
 /// Side panel displaying the full details of a selected news article.
 ///
@@ -27,6 +29,9 @@ pub fn ArticleDetail(
     #[props(default = false)] is_chatting: bool,
     on_chat_send: EventHandler<String>,
 ) -> Element {
+    let locale = use_context::<Signal<Locale>>();
+    let l = *locale.read();
+
     let css_suffix = card.category.to_lowercase().replace(' ', "-");
     let badge_class = format!("news-badge news-badge--{css_suffix}");
     let mut chat_input = use_signal(String::new);
@@ -41,7 +46,7 @@ pub fn ArticleDetail(
             button {
                 class: "article-detail-close",
                 onclick: move |_| on_close.call(()),
-                "X"
+                "{t(l, \"common.close\")}"
             }
 
             div { class: "article-detail-content",
@@ -74,7 +79,7 @@ pub fn ArticleDetail(
                     href: "{card.url}",
                     target: "_blank",
                     rel: "noopener",
-                    "Read original article"
+                    "{t(l, \"article.read_original\")}"
                 }
 
                 // AI Summary bubble (below the link)
@@ -82,11 +87,11 @@ pub fn ArticleDetail(
                     if is_summarizing {
                         div { class: "ai-summary-bubble-loading",
                             div { class: "ai-summary-dot-pulse" }
-                            span { "Summarizing..." }
+                            span { "{t(l, \"article.summarizing\")}" }
                         }
                     } else if let Some(ref text) = summary {
                         p { class: "ai-summary-bubble-text", "{text}" }
-                        span { class: "ai-summary-bubble-label", "Summarized with AI" }
+                        span { class: "ai-summary-bubble-label", "{t(l, \"article.summarized_with_ai\")}" }
                     }
                 }
 
@@ -123,7 +128,7 @@ pub fn ArticleDetail(
                             input {
                                 class: "article-chat-textbox",
                                 r#type: "text",
-                                placeholder: "Ask a follow-up question...",
+                                placeholder: "{t(l, \"article.ask_followup\")}",
                                 value: "{chat_input}",
                                 disabled: is_chatting,
                                 oninput: move |e| chat_input.set(e.value()),
@@ -147,7 +152,7 @@ pub fn ArticleDetail(
                                         chat_input.set(String::new());
                                     }
                                 },
-                                "Send"
+                                "{t(l, \"common.send\")}"
                             }
                         }
                     }