chore: archive completed proposals

Archive two completed proposals:
- enable-audit-logging: Added audit logging for auth, task, and admin events
- simplify-frontend-add-billing: Removed Export/Settings pages, added translation stats

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2025-12-14-simplify-frontend-add-billing/specs/frontend-ui/spec.md

@@ -0,0 +1,31 @@
+# Spec Delta: frontend-ui
+
+## REMOVED Requirements
+
+- REQ-FE-EXPORT: Export Page - The export page for batch exporting task results is removed.
+- REQ-FE-SETTINGS: Settings Page - The settings page for managing export rules is removed.
+
+## ADDED Requirements
+
+### Requirement: Translation Statistics in Admin Dashboard
+The admin dashboard SHALL display translation usage statistics and estimated costs.
+
+#### Scenario: Admin views translation statistics
+- GIVEN the user is logged in as admin
+- WHEN the user views the admin dashboard
+- THEN the page displays a translation statistics card showing:
+  - Total translation count
+  - Total token usage (input + output tokens)
+  - Estimated cost based on token pricing
+  - Breakdown by target language
+
+## MODIFIED Requirements
+
+### Requirement: Navigation Menu Updated
+The navigation menu SHALL be updated to remove Export and Settings links.
+
+#### Scenario: User views navigation menu
+- GIVEN the user is logged in
+- WHEN the user views the sidebar navigation
+- THEN the menu shows: Upload, Processing, Results, Task History, Admin (if admin)
+- AND the menu does NOT show: Export, Settings