feat(i18n): add Russian translations + replace Frappe branding with IIE

Branding:
- 'Powered by Learning' -> 'Powered by IIE' (sidebar tooltip)
- 'Frappe Learning' -> 'IIE' (HelpModal title, email templates)
- frappe.io URLs -> enlightrussia.ru
- 'Install Frappe Learning' -> 'Установить приложение IIE'
- PersonaForm question translated

Translations (ru.po):
- Added 125 new Russian translations for client-facing strings
- Covers: sidebar nav, profiles, leaderboard, points, lessons,
  batches, assignments, error messages, video stats, MPGU-specific

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/Modals/EmailTemplateModal.vue

@@ -48,7 +48,7 @@
 					:rows="10"
 					:placeholder="
 						__(
-							'<p>Dear {{ member_name }},</p>\n\n<p>You have been enrolled in our upcoming batch {{ batch_name }}.</p>\n\n<p>Thanks,</p>\n<p>Frappe Learning</p>'
+							'<p>Dear {{ member_name }},</p>\n\n<p>You have been enrolled in our upcoming batch {{ batch_name }}.</p>\n\n<p>Thanks,</p>\n<p>IIE</p>'
 						)
 					"
 				/>
@@ -64,7 +64,7 @@
 						:fixedMenu="true"
 						:placeholder="
 							__(
-								'Dear {{ member_name }},\n\nYou have been enrolled in our upcoming batch {{ batch_name }}.\n\nThanks,\nFrappe Learning'
+								'Dear {{ member_name }},\n\nYou have been enrolled in our upcoming batch {{ batch_name }}.\n\nThanks,\nIIE'
 							)
 						"
 						editorClass="prose-sm max-w-none border-b border-x border-outline-gray-modals bg-surface-gray-2 rounded-b-md py-1 px-2 min-h-[7rem] max-h-[18rem] overflow-y-auto"