feat: Vendor-level consent + Consent analytics (F4 + F6)

F4: Granular Vendor-Level Consent
- Migration 113: vendor_consents JSONB on banner_consents + audit_log
- ConsentCreate schema + BannerConsentDB model extended
- banner_consent_service stores vendor_consents alongside categories
- Audit trail includes vendor-level decisions + user_agent

F6: Consent Rate Analytics
- Migration 114: user_agent on audit_log + time-series index
- BannerAnalyticsService: time series, category breakdown, device stats
- banner_analytics_routes: 4 endpoints (overview, time-series, categories, devices)
- AnalyticsDashboard.tsx: KPIs, bar chart, category bars, device breakdown
- New "Analytik" tab in cookie-banner page

[migration-approved]

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/migrations/114_banner_analytics.sql

@@ -0,0 +1,8 @@
+-- Migration 114: Banner Analytics Enrichment
+-- Adds user_agent to audit log for device classification + time-series index
+
+ALTER TABLE compliance_banner_consent_audit_log
+    ADD COLUMN IF NOT EXISTS user_agent TEXT;
+
+CREATE INDEX IF NOT EXISTS idx_banner_audit_timeseries
+    ON compliance_banner_consent_audit_log(tenant_id, site_id, action, created_at);