refactor: implement template-driven node tree and human-readable vault layout

Unified Node model: added template_id, fs_path, archived, sort_order fields.
Template registry: system templates embedded as JSON (folder/project/client/
document/recipe), with Registry for enabled/disabled/filtered access.
SafeDisplayNameToPathSegment: human-readable path segments with Cyrillic
support, illegal char replacement, uniqueness via numeric suffixes.
Sidebar refactored: system views (Today/Inbox/Activity) separate from
workspace tree. Creation menu built dynamically from enabled templates.
Create/Rename/Move: physical folder operations with fs_path update,
recursive descendant path updates.
DB migration 012: adds template_id, fs_path, archived columns.
Vault migration command: rebuilds fs_path for existing nodes.
Tests: safename, registry, node model, repository integration.
Docs: VAULT_LAYOUT.md, TEMPLATES.md, PLAN.md updated.
i18n: nav.system, nav.workspace, template.*, common.rename/archive,
migrate.* keys added to ru.json and en.json.

frontend/src/lib/i18n/locales/en.js

@@ -7,6 +7,11 @@ export default {
   'nav.recipes': 'Recipes',
   'nav.documents': 'Documents',
   'nav.archive': 'Archive',
+  'nav.system': 'System',
+  'nav.workspace': 'Workspace',
+  'nav.noNodes': 'No nodes',
+  'nav.openFolder': 'Open folder',
+  'nav.createInside': 'Create inside',
 
   'tab.overview': 'Overview',
   'tab.notes': 'Notes',

frontend/src/lib/i18n/locales/ru.js

@@ -15,6 +15,11 @@ export default {
   'nav.syncNow': 'Синхронизировать',
   'nav.selectPrompt': 'Выберите раздел или дело',
   'nav.brand': 'Верстак',
+  'nav.system': 'Системное',
+  'nav.workspace': 'Рабочее пространство',
+  'nav.noNodes': 'Нет узлов',
+  'nav.openFolder': 'Открыть папку',
+  'nav.createInside': 'Создать внутри',
 
   'tab.overview': 'Обзор',
   'tab.notes': 'Заметки',