feat: Implement map analytics system with effectiveness tracking

Add complete map analytics pipeline to answer: "Which maps drive the most
players? Is my rotation working?"

Backend Changes:
- Migration 005: Add map_id FK to server_stats and wipe_history tables
- Stats consumer now captures current_map_id when persisting stats
- Map analytics queries: get_map_analytics() returns performance metrics,
  effectiveness scores, and rotation health
- API endpoint: GET /api/analytics/maps?range=90d returns summary with
  best performing map and rotation effectiveness percentage

Frontend Changes:
- MapAnalyticsView.vue: Complete dashboard with performance charts,
  sortable metrics table, actionable insights, and CSV export
- ECharts bar chart comparing avg vs peak players per map
- Color-coded effectiveness scoring (green ≥80%, yellow ≥60%, red <60%)
- Time range selector: 30d/90d/all

Purpose: Enables data-driven map selection for wipe day based on player
engagement metrics. Rotation effectiveness algorithm scores maps by
(avg_players / peak_players) * 100.

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

backend/migrations/005_map_analytics.sql

@@ -0,0 +1,15 @@
+-- Map Analytics — Add FK tracking for map effectiveness metrics
+-- Phase 2.2 Feature: Track which maps drive player count and rotation effectiveness
+
+-- Add map_id to server_stats to correlate player counts with specific maps
+ALTER TABLE server_stats ADD COLUMN map_id UUID REFERENCES map_library(id) ON DELETE SET NULL;
+CREATE INDEX idx_server_stats_map ON server_stats(map_id);
+
+-- Migrate wipe_history from string to FK (preserve legacy data for backward compat)
+ALTER TABLE wipe_history ADD COLUMN map_id UUID REFERENCES map_library(id) ON DELETE SET NULL;
+ALTER TABLE wipe_history RENAME COLUMN map_used TO map_used_legacy;
+CREATE INDEX idx_wipe_history_map ON wipe_history(map_id);
+
+COMMENT ON COLUMN server_stats.map_id IS 'FK to map_library — tracks which map was active when stats were recorded';
+COMMENT ON COLUMN wipe_history.map_id IS 'FK to map_library — tracks which map was used for this wipe';
+COMMENT ON COLUMN wipe_history.map_used_legacy IS 'Legacy string-based map name (preserved from pre-005 data)';