test: add service tests and fix architecture violations

- Add comprehensive unit tests for FeatureService (24 tests)
- Add comprehensive unit tests for UsageService (11 tests)
- Fix API-002/API-003 architecture violations in feature/usage APIs
- Move database queries from API layer to service layer
- Create UsageService for usage and limits management
- Create custom exceptions (FeatureNotFoundError, TierNotFoundError)
- Fix ValidationException usage in content_pages.py
- Refactor vendor features API to use proper response models
- All 35 new tests passing

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

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

app/exceptions/__init__.py

@@ -263,6 +263,13 @@ from .onboarding import (
     OnboardingSyncNotCompleteException,
 )
 
+# Feature management exceptions
+from .feature import (
+    FeatureNotFoundError,
+    InvalidFeatureCodesError,
+    TierNotFoundError,
+)
+
 __all__ = [
     # Base exceptions
     "WizamartException",
@@ -456,4 +463,8 @@ __all__ = [
     "OnboardingCsvUrlRequiredException",
     "OnboardingSyncJobNotFoundException",
     "OnboardingSyncNotCompleteException",
+    # Feature exceptions
+    "FeatureNotFoundError",
+    "TierNotFoundError",
+    "InvalidFeatureCodesError",
 ]

app/exceptions/feature.py

@@ -0,0 +1,42 @@
+# app/exceptions/feature.py
+"""
+Feature management exceptions.
+"""
+
+from app.exceptions.base import ResourceNotFoundException, ValidationException
+
+
+class FeatureNotFoundError(ResourceNotFoundException):
+    """Feature not found."""
+
+    def __init__(self, feature_code: str):
+        super().__init__(
+            resource_type="Feature",
+            identifier=feature_code,
+            message=f"Feature '{feature_code}' not found",
+        )
+        self.feature_code = feature_code
+
+
+class TierNotFoundError(ResourceNotFoundException):
+    """Subscription tier not found."""
+
+    def __init__(self, tier_code: str):
+        super().__init__(
+            resource_type="SubscriptionTier",
+            identifier=tier_code,
+            message=f"Tier '{tier_code}' not found",
+        )
+        self.tier_code = tier_code
+
+
+class InvalidFeatureCodesError(ValidationException):
+    """Invalid feature codes provided."""
+
+    def __init__(self, invalid_codes: set[str]):
+        codes_str = ", ".join(sorted(invalid_codes))
+        super().__init__(
+            message=f"Invalid feature codes: {codes_str}",
+            details={"invalid_codes": list(invalid_codes)},
+        )
+        self.invalid_codes = invalid_codes