feat: add UI usage analytics tracking

Tracks authenticated UI user requests to understand usage patterns:
- New ClickHouse usage_events table with 90-day TTL
- UsageTrackingInterceptor captures method, path, duration, user
- Path normalization groups dynamic segments ({id}, {hash})
- Buffered writes via WriteBuffer + periodic flush
- Admin endpoint GET /api/v1/admin/usage with groupBy=endpoint|user|hour
- Skips agent requests, health checks, and data ingestion

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

cameleer3-server-app/src/main/resources/clickhouse/V10__usage_events.sql

@@ -0,0 +1,13 @@
+CREATE TABLE IF NOT EXISTS usage_events (
+    timestamp    DateTime64(3) DEFAULT now64(3),
+    username     LowCardinality(String),
+    method       LowCardinality(String),
+    path         String,
+    normalized   LowCardinality(String),
+    status_code  UInt16,
+    duration_ms  UInt32,
+    query_params String DEFAULT ''
+)
+ENGINE = MergeTree()
+ORDER BY (username, timestamp)
+TTL toDateTime(timestamp) + INTERVAL 90 DAY;