fix(i18n): replace fragment translation keys with placeholder-based complete sentences

- Use {gravatar} placeholder in profile.avatar_upload_hint for proper i18n
- Use {settings_link} placeholder in subscription.single_user_body
- Use {api_tokens_link} placeholder in integrations.webhook_step1
- Add optional chaining in common.js for window.__i18n safety

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/templates/integrations_dashboard.html

@@ -846,8 +846,8 @@
               </h4>
               <ol class="text-sm text-gray-600 dark:text-gray-400 space-y-2 list-decimal list-inside">
                 <li>
-                  Go to <a href="/api-tokens" class="text-indigo-600 hover:underline font-medium">API Tokens</a>
-                  {{ _("integrations.webhook_create_token") }}
+                  {% set api_tokens_link %}<a href="/api-tokens" class="text-indigo-600 hover:underline font-medium">{{ _("nav.api_tokens") }}</a>{% endset %}
+                  {{ _("integrations.webhook_step1", api_tokens_link=api_tokens_link) | safe }}
                 </li>
                 <li>{{ _("integrations.webhook_upload_with_token") }}</li>
               </ol>

frontend/templates/profile.html

@@ -77,7 +77,8 @@
       <!-- Upload controls -->
       <div class="flex-1 space-y-3">
         <p class="text-sm text-gray-600 dark:text-gray-400">
-          {{ _("profile.avatar_upload_hint") }} <a href="https://gravatar.com" class="underline" target="_blank" rel="noopener noreferrer" aria-label="{{ _('profile.gravatar_link') }} (opens in new tab)">{{ _("profile.gravatar_link") }}</a> {{ _("profile.avatar_gravatar_suffix") }}
+          {% set gravatar_anchor %}<a href="https://gravatar.com" class="underline" target="_blank" rel="noopener noreferrer" aria-label="{{ _('profile.gravatar_link') }} (opens in new tab)">{{ _("profile.gravatar_link") }}</a>{% endset %}
+          {{ _("profile.avatar_upload_hint", gravatar=gravatar_anchor) | safe }}
         </p>
         <label
           for="avatar-input"

frontend/templates/subscription.html

@@ -23,8 +23,8 @@
     <div>
       <p class="font-semibold text-blue-800">{{ _("subscription.single_user_title") }}</p>
       <p class="text-blue-700 text-sm mt-1">
-        {{ _("subscription.single_user_body_before_link") }}
-        <a href="/settings" class="underline hover:text-blue-900">{{ _("nav.settings") }}</a>{{ _("subscription.single_user_body_after_link") }}
+        {% set settings_link %}<a href="/settings" class="underline hover:text-blue-900">{{ _("nav.settings") }}</a>{% endset %}
+        {{ _("subscription.single_user_body", settings_link=settings_link) | safe }}
       </p>
     </div>
   </div>