feat(i18n): add i18n on server side

- remove the hardcoded list of locales in favor of a discovry on start time
    - server will stop on badly formatted locale .json
    - add server.* entries for serer side translation

    server side translation will be used for templating and email
    note: no json in some embded html (like in /magic), amount of work was similar

src/domain/services/i18n_service.rs

@@ -1,5 +1,20 @@
+//! Domain port for translation lookup.
+//!
+//! The concrete locale type lives in [`crate::common::locale::Locale`] and
+//! is a string-backed newtype validated at construction against a
+//! [`LocaleRegistry`] populated at startup from `static/locales/*.json`.
+//!
+//! This module is a thin facade: the trait + error types stay where the
+//! application + infrastructure layers expect them; the type itself is
+//! re-exported from `common` so the same `Locale` value flows through
+//! handlers, middleware, services, and DTOs without re-wrapping.
+//!
+//! [`LocaleRegistry`]: crate::common::locale::LocaleRegistry
+
 use thiserror::Error;
 
+pub use crate::common::locale::Locale;
+
 /// Error types for i18n service operations
 #[derive(Debug, Error)]
 pub enum I18nError {
@@ -16,53 +31,37 @@ pub enum I18nError {
 /// Result type for i18n service operations
 pub type I18nResult<T> = Result<T, I18nError>;
 
-/// Supported locales
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
-pub enum Locale {
-    #[default]
-    English,
-    Spanish,
-    French,
-    German,
-    Portuguese,
-}
-
-impl Locale {
-    /// Convert locale to code string
-    pub fn as_str(&self) -> &'static str {
-        match self {
-            Locale::English => "en",
-            Locale::Spanish => "es",
-            Locale::French => "fr",
-            Locale::German => "de",
-            Locale::Portuguese => "pt",
-        }
-    }
-
-    /// Create from locale code string
-    pub fn from_code(code: &str) -> Option<Self> {
-        match code.to_lowercase().as_str() {
-            "en" => Some(Locale::English),
-            "es" => Some(Locale::Spanish),
-            "fr" => Some(Locale::French),
-            "de" => Some(Locale::German),
-            "pt" => Some(Locale::Portuguese),
-            _ => None,
-        }
-    }
-}
-
-/// Interface for i18n service (primary port)
+/// Interface for i18n service (primary port).
+///
+/// Implementations should fall back to English when the requested
+/// locale has no entry for `key`. Unknown locales (codes not in the
+/// configured [`crate::common::locale::LocaleRegistry`]) are an
+/// `InvalidLocale` error — callers normally avoid this by going
+/// through the registry's `parse_or_default` before calling
+/// `translate`.
 pub trait I18nService: Send + Sync + 'static {
-    /// Get a translation for a key and locale
+    /// Get a translation for a key and locale.
     async fn translate(&self, key: &str, locale: Locale) -> I18nResult<String>;
 
-    /// Load translations for a locale
+    /// Get a translation with `{{name}}`-mustache substitution applied
+    /// to the resolved string. Mirrors the frontend convention in
+    /// `static/js/core/i18n.js:117` so JSON values are interchangeable
+    /// between front- and back-end.
+    async fn translate_args(
+        &self,
+        key: &str,
+        locale: Locale,
+        args: &[(&str, &str)],
+    ) -> I18nResult<String>;
+
+    /// Load translations for a locale into the in-memory cache.
     async fn load_translations(&self, locale: Locale) -> I18nResult<()>;
 
-    /// Get available locales
+    /// Available locales — typically the contents of the underlying
+    /// registry. Returned in arbitrary order; callers that need a
+    /// stable order should sort.
     async fn available_locales(&self) -> Vec<Locale>;
 
-    /// Check if a locale is supported
+    /// True iff the given locale is in the registry.
     async fn is_supported(&self, locale: Locale) -> bool;
 }