feat: complete analytics module self-containment

Migrate analytics module to fully self-contained structure:

- routes/api/vendor.py - API endpoints
- routes/pages/vendor.py - Page routes with full implementation
- services/stats_service.py - Business logic (moved from app/services)
- services/usage_service.py - Usage tracking (moved from app/services)
- schemas/stats.py - Pydantic schemas (moved from models/schema)
- models/__init__.py - Model exports
- templates/analytics/vendor/ - Templates (moved from app/templates)
- static/vendor/js/ - JavaScript (moved from static/vendor)
- locales/ - Translations (en, de, fr, lu)
- exceptions.py - Module exceptions

Removed legacy files:
- app/modules/analytics/routes/vendor.py (replaced by routes/pages/)
- static/admin/js/analytics.js (unused)

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

app/modules/analytics/exceptions.py

@@ -0,0 +1,39 @@
+# app/modules/analytics/exceptions.py
+"""
+Analytics module exceptions.
+
+Module-specific exceptions for analytics functionality.
+"""
+
+from app.exceptions.base import (
+    BusinessLogicException,
+    ValidationException,
+)
+
+
+class ReportGenerationException(BusinessLogicException):
+    """Raised when report generation fails."""
+
+    def __init__(self, report_type: str, reason: str):
+        super().__init__(
+            message=f"Failed to generate {report_type} report: {reason}",
+            error_code="REPORT_GENERATION_FAILED",
+        )
+
+
+class InvalidDateRangeException(ValidationException):
+    """Raised when an invalid date range is provided."""
+
+    def __init__(self, start_date: str, end_date: str):
+        super().__init__(
+            message=f"Invalid date range: {start_date} to {end_date}",
+            field="date_range",
+            value=f"{start_date} - {end_date}",
+        )
+        self.error_code = "INVALID_DATE_RANGE"
+
+
+__all__ = [
+    "ReportGenerationException",
+    "InvalidDateRangeException",
+]