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/organization/mod.rs

@@ -8,6 +8,7 @@ use dioxus::prelude::*;
 
 use crate::app::Route;
 use crate::components::sub_nav::{SubNav, SubNavItem};
+use crate::i18n::{t, Locale};
 
 /// Shell layout for the Organization section.
 ///
@@ -15,13 +16,16 @@ use crate::components::sub_nav::{SubNav, SubNavItem};
 /// the child route outlet. Sits inside the main `AppShell` layout.
 #[component]
 pub fn OrgShell() -> Element {
+    let locale = use_context::<Signal<Locale>>();
+    let l = *locale.read();
+
     let tabs = vec![
         SubNavItem {
-            label: "Pricing",
+            label: t(l, "nav.pricing"),
             route: Route::OrgPricingPage {},
         },
         SubNavItem {
-            label: "Dashboard",
+            label: t(l, "nav.dashboard"),
             route: Route::OrgDashboardPage {},
         },
     ];