feat(analytics): add tabbed layout with coverage heatmap

Add Phase 5 types (CoverageResponse, FlowQualityResponse, EnhancedPsaMetrics)
and API methods. Refactor FlowPilotAnalyticsPage with tab bar (Overview,
Coverage, Flow Quality, PSA) with lazy data loading. Create CoverageHeatmap
component with color-coded resolution/escalation/guided rate cells.

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

frontend/src/types/flowpilot-analytics.ts

@@ -77,3 +77,60 @@ export interface KnowledgeGapReport {
   generated_at: string
   gaps: KnowledgeGap[]
 }
+
+// Phase 5 — Coverage
+export interface CoverageDomainRow {
+  domain: string
+  flow_count: number
+  session_count: number
+  resolution_rate: number
+  escalation_rate: number
+  guided_rate: number
+  avg_resolution_minutes: number | null
+}
+
+export interface CoverageResponse {
+  domains: CoverageDomainRow[]
+  unmapped_session_count: number
+  total_domains: number
+}
+
+// Phase 5 — Flow Quality
+export interface FlowQualityRow {
+  flow_id: string
+  name: string
+  tree_type: string
+  usage_count: number
+  success_rate: number | null
+  last_matched_at: string | null
+  avg_confidence: number | null
+  quality_score: number
+}
+
+export interface FlowQualityResponse {
+  flows: FlowQualityRow[]
+  top_performers: FlowQualityRow[]
+  needs_attention: FlowQualityRow[]
+}
+
+// Phase 5 — Enhanced PSA
+export interface PsaFunnel {
+  total_sessions: number
+  linked_to_ticket: number
+  doc_pushed: number
+  time_entry_logged: number
+}
+
+export interface PsaDailyTrend {
+  date: string
+  entries: number
+  hours: number
+}
+
+export interface EnhancedPsaMetrics {
+  total_time_entries: number
+  total_hours_logged: number
+  avg_hours_per_session: number
+  push_funnel: PsaFunnel
+  daily_trend: PsaDailyTrend[]
+}