feat(frontend): add admin/tools pages, i18n, UI improvements, route annotations

New pages:
- /admin: admin overview page with links to user/role/settings/LLM management
- /tools: tools overview page with links to mapper/debug/storage/backup tools

i18n:
- nav.json (en/ru): add description keys for admin and tools sub-items
- migration.json (en/ru): add help tooltips and step-by-step instructions
  for the database mapping workflow

UI components:
- EnvSelector: add optional helpText with HelpTooltip
- MappingTable: add HelpTooltip for status column
- MultiSelect: add id for accessibility, fix label element structure
- Input: fix reactive id assignment with ()
- Select: fix reactive id assignment with ()

Routes:
- routes.ts: add admin.overview() and tools.overview() routes
- dashboards/+page.svelte: add @RELATION BINDS_TO annotation
- migration/mappings/+page.svelte: add HelpTooltip, Card imports, help texts
- translate pages: minor annotation updates

Other:
- .gitignore: add backend/:memory (SQLite test artifact)

.gitignore

@@ -70,6 +70,7 @@ backend/auth.db
 semantics/reports
 backend/**/*.db
 backend/**/*.sqlite
+backend/:memory
 
 # Universal / tooling
 node_modules/