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

example.env

@@ -416,6 +416,31 @@ OXICLOUD_WOPI_ENABLED=false
 # IdP is the security boundary and may enforce MFA we shouldn't bypass.
 #OXICLOUD_MAGIC_LINK_OPEN_TO_PASSWORD_USERS=false
 
+# -----------------------------------------------------------------------------
+# INTERNATIONALIZATION (server-rendered surfaces)
+# -----------------------------------------------------------------------------
+#
+# Default locale for server-rendered HTML pages and outbound emails when
+# no stronger signal is available. The resolution priority is:
+#
+#   HTML pages (anonymous, e.g. magic-link landing):
+#     1. ?lang=xx query override
+#     2. browser Accept-Language header (q-weighted)
+#     3. this default
+#
+#   Emails to a known user:
+#     1. user.preferred_locale column
+#     2. this default
+#
+# Supported locales are discovered at boot by listing static/locales/*.json,
+# so adding a 17th locale is a file-drop operation (no rebuild required).
+# This variable must match one of the discovered codes — startup fails fast
+# if you set OXICLOUD_DEFAULT_LOCALE=xx and no static/locales/xx.json exists.
+#
+# Default: "en". Today's shipped locales: ar, de, en, es, fa, fr, hi, it,
+# ja, ko, nl, pl, pt, ru, zh, zh-TW.
+#OXICLOUD_DEFAULT_LOCALE=en
+
 # -----------------------------------------------------------------------------
 # PROXY
 # -----------------------------------------------------------------------------