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/login.rs

@@ -1,6 +1,8 @@
-use crate::Route;
 use dioxus::prelude::*;
 
+use crate::i18n::{t, Locale};
+use crate::Route;
+
 /// Login redirect component.
 ///
 /// Redirects the user to the external OAuth authentication endpoint.
@@ -12,6 +14,8 @@ use dioxus::prelude::*;
 #[component]
 pub fn Login(redirect_url: String) -> Element {
     let navigator = use_navigator();
+    let locale = use_context::<Signal<Locale>>();
+    let l = *locale.read();
 
     use_effect(move || {
         // Default to /dashboard when redirect_url is empty.
@@ -25,6 +29,6 @@ pub fn Login(redirect_url: String) -> Element {
     });
 
     rsx!(
-        div { class: "text-center p-6", "Redirecting to secure login page…" }
+        div { class: "text-center p-6", "{t(l, \"auth.redirecting_secure\")}" }
     )
 }