feat: A/B Testing + Compliance Report PDF (F5 + F8)

F5: A/B Testing for Consent Rate
- Migration 116: banner_variants table + variant tracking in audit log
- BannerABService: deterministic sticky bucketing via device hash,
  chi-squared significance testing, variant CRUD
- banner_ab_routes: 6 endpoints (CRUD + stats + assign)
- ABTestPanel.tsx: variant creation, traffic sliders, opt-in comparison
  chart with winner/significance badges
- New "A/B-Test" tab in cookie-banner page

F8: Compliance Report PDF
- CompliancePDFGenerator: reportlab-based A4 PDF covering all modules
  (Company Profile, TOM, VVT, DSFA, Risks, Vendors, Incidents,
  Reviews, Consents, Roles)
- compliance_report_routes: GET /compliance/report/pdf
- "Compliance-Report herunterladen" button on SDK dashboard

[migration-approved]

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

backend-compliance/migrations/116_banner_ab_testing.sql

@@ -0,0 +1,31 @@
+-- Migration 116: Banner A/B Testing
+-- Enables variant testing for consent rate optimization
+
+CREATE TABLE IF NOT EXISTS compliance_banner_variants (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    tenant_id UUID NOT NULL,
+    site_config_id UUID NOT NULL,
+    variant_name VARCHAR(100) NOT NULL,
+    variant_key VARCHAR(20) NOT NULL,
+    traffic_percent INT NOT NULL DEFAULT 50 CHECK (traffic_percent BETWEEN 0 AND 100),
+    is_control BOOLEAN NOT NULL DEFAULT FALSE,
+    banner_title TEXT,
+    banner_description TEXT,
+    position VARCHAR(20),
+    style VARCHAR(20),
+    primary_color VARCHAR(20),
+    show_decline_all BOOLEAN,
+    theme_overrides JSONB DEFAULT '{}',
+    is_active BOOLEAN NOT NULL DEFAULT TRUE,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ DEFAULT NOW(),
+    UNIQUE(site_config_id, variant_key)
+);
+
+CREATE INDEX IF NOT EXISTS idx_banner_variants_site
+    ON compliance_banner_variants(site_config_id);
+
+ALTER TABLE compliance_banner_consent_audit_log
+    ADD COLUMN IF NOT EXISTS variant_id UUID;
+ALTER TABLE compliance_banner_consent_audit_log
+    ADD COLUMN IF NOT EXISTS variant_key VARCHAR(20);