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/pages/impressum.rs

@@ -2,6 +2,7 @@ use dioxus::prelude::*;
 use dioxus_free_icons::icons::bs_icons::BsShieldCheck;
 use dioxus_free_icons::Icon;
 
+use crate::i18n::{t, Locale};
 use crate::Route;
 
 /// Impressum (legal notice) page required by German/EU law.
@@ -10,6 +11,9 @@ use crate::Route;
 /// accessible without authentication.
 #[component]
 pub fn ImpressumPage() -> Element {
+    let locale = use_context::<Signal<Locale>>();
+    let l = *locale.read();
+
     rsx! {
         div { class: "legal-page",
             nav { class: "legal-nav",
@@ -21,53 +25,53 @@ pub fn ImpressumPage() -> Element {
                 }
             }
             main { class: "legal-content",
-                h1 { "Impressum" }
+                h1 { "{t(l, \"impressum.title\")}" }
 
-                h2 { "Information according to 5 TMG" }
+                h2 { "{t(l, \"impressum.info_tmg\")}" }
                 p {
-                    "CERTifAI GmbH"
+                    "{t(l, \"impressum.company\")}"
                     br {}
-                    "Musterstrasse 1"
+                    "{t(l, \"impressum.address_street\")}"
                     br {}
-                    "10115 Berlin"
+                    "{t(l, \"impressum.address_city\")}"
                     br {}
-                    "Germany"
+                    "{t(l, \"impressum.address_country\")}"
                 }
 
-                h2 { "Represented by" }
-                p { "Managing Director: [Name]" }
+                h2 { "{t(l, \"impressum.represented_by\")}" }
+                p { "{t(l, \"impressum.managing_director\")}" }
 
-                h2 { "Contact" }
+                h2 { "{t(l, \"impressum.contact\")}" }
                 p {
-                    "Email: info@certifai.example"
+                    "{t(l, \"impressum.email\")}"
                     br {}
-                    "Phone: +49 (0) 30 1234567"
+                    "{t(l, \"impressum.phone\")}"
                 }
 
-                h2 { "Commercial Register" }
+                h2 { "{t(l, \"impressum.commercial_register\")}" }
                 p {
-                    "Registered at: Amtsgericht Berlin-Charlottenburg"
+                    "{t(l, \"impressum.registered_at\")}"
                     br {}
-                    "Registration number: HRB XXXXXX"
+                    "{t(l, \"impressum.registration_number\")}"
                 }
 
-                h2 { "VAT ID" }
-                p { "VAT identification number according to 27a UStG: DE XXXXXXXXX" }
+                h2 { "{t(l, \"impressum.vat_id\")}" }
+                p { "{t(l, \"impressum.vat_number\")}" }
 
-                h2 { "Responsible for content according to 55 Abs. 2 RStV" }
+                h2 { "{t(l, \"impressum.responsible_content\")}" }
                 p {
                     "[Name]"
                     br {}
-                    "CERTifAI GmbH"
+                    "{t(l, \"impressum.company\")}"
                     br {}
-                    "Musterstrasse 1"
+                    "{t(l, \"impressum.address_street\")}"
                     br {}
-                    "10115 Berlin"
+                    "{t(l, \"impressum.address_city\")}"
                 }
             }
             footer { class: "legal-footer",
-                Link { to: Route::LandingPage {}, "Back to Home" }
-                Link { to: Route::PrivacyPage {}, "Privacy Policy" }
+                Link { to: Route::LandingPage {}, "{t(l, \"common.back_to_home\")}" }
+                Link { to: Route::PrivacyPage {}, "{t(l, \"common.privacy_policy\")}" }
             }
         }
     }