feat: add comprehensive tier-based feature management system

Implement database-driven feature gating with contextual upgrade prompts:

- Add Feature model with 30 features across 8 categories
- Create FeatureService with caching for tier-based feature checking
- Add @require_feature decorator and RequireFeature dependency for backend enforcement
- Create vendor features API (6 endpoints) and admin features API
- Add Alpine.js feature store and upgrade prompts store for frontend
- Create Jinja macros: feature_gate, feature_locked, limit_warning, usage_bar
- Add usage API for tracking orders/products/team limits with upgrade info
- Fix Stripe webhook to create VendorAddOn records on addon purchase
- Integrate upgrade prompts into vendor dashboard with tier badge and usage bars

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

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

app/api/v1/vendor/analytics.py

@@ -4,6 +4,10 @@ Vendor analytics and reporting endpoints.
 
 Vendor Context: Uses token_vendor_id from JWT token (authenticated vendor API pattern).
 The get_current_vendor_api dependency guarantees token_vendor_id is present.
+
+Feature Requirements:
+- basic_reports: Basic analytics (Essential tier)
+- analytics_dashboard: Advanced analytics (Business tier)
 """
 
 import logging
@@ -13,7 +17,9 @@ from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_vendor_api
 from app.core.database import get_db
+from app.core.feature_gate import RequireFeature
 from app.services.stats_service import stats_service
+from models.database.feature import FeatureCode
 from models.database.user import User
 from models.schema.stats import (
     VendorAnalyticsCatalog,
@@ -31,6 +37,7 @@ def get_vendor_analytics(
     period: str = Query("30d", description="Time period: 7d, 30d, 90d, 1y"),
     current_user: User = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
+    _: None = Depends(RequireFeature(FeatureCode.BASIC_REPORTS, FeatureCode.ANALYTICS_DASHBOARD)),
 ):
     """Get vendor analytics data for specified time period."""
     data = stats_service.get_vendor_analytics(db, current_user.token_vendor_id, period)