Add comparison stats: failure rate %, vs-yesterday change, today total

Stats endpoint now returns current + previous period (24h shift) values
plus today's total count. UI shows:
- Total Matches: "of 12.3K today"
- Avg Duration: arrow + % vs yesterday
- Failure Rate: percentage of errors vs total, arrow + % vs yesterday
- P99 Latency: arrow + % vs yesterday
- In-Flight: unchanged (running executions)

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

cameleer3-server-app/src/main/java/com/cameleer3/server/app/search/ClickHouseSearchEngine.java

@@ -89,18 +89,48 @@ public class ClickHouseSearchEngine implements SearchEngine {
 
     @Override
     public ExecutionStats stats(Instant from, Instant to) {
-        return jdbcTemplate.queryForObject(
-                "SELECT countIf(status = 'FAILED') AS failed_count, " +
+        String aggregateSql = "SELECT count() AS total_count, " +
+                "countIf(status = 'FAILED') AS failed_count, " +
                 "toInt64(avg(duration_ms)) AS avg_duration_ms, " +
                 "toInt64(quantile(0.99)(duration_ms)) AS p99_duration_ms, " +
                 "countIf(status = 'RUNNING') AS active_count " +
-                "FROM route_executions WHERE start_time >= ? AND start_time <= ?",
-                (rs, rowNum) -> new ExecutionStats(
+                "FROM route_executions WHERE start_time >= ? AND start_time <= ?";
+
+        // Current period
+        record PeriodStats(long totalCount, long failedCount, long avgDurationMs, long p99LatencyMs, long activeCount) {}
+        PeriodStats current = jdbcTemplate.queryForObject(aggregateSql,
+                (rs, rowNum) -> new PeriodStats(
+                        rs.getLong("total_count"),
                         rs.getLong("failed_count"),
                         rs.getLong("avg_duration_ms"),
                         rs.getLong("p99_duration_ms"),
                         rs.getLong("active_count")),
                 Timestamp.from(from), Timestamp.from(to));
+
+        // Previous period (same window shifted back 24h)
+        Duration window = Duration.between(from, to);
+        Instant prevFrom = from.minus(Duration.ofHours(24));
+        Instant prevTo = prevFrom.plus(window);
+        PeriodStats prev = jdbcTemplate.queryForObject(aggregateSql,
+                (rs, rowNum) -> new PeriodStats(
+                        rs.getLong("total_count"),
+                        rs.getLong("failed_count"),
+                        rs.getLong("avg_duration_ms"),
+                        rs.getLong("p99_duration_ms"),
+                        rs.getLong("active_count")),
+                Timestamp.from(prevFrom), Timestamp.from(prevTo));
+
+        // Today total (midnight UTC to now)
+        Instant todayStart = Instant.now().truncatedTo(java.time.temporal.ChronoUnit.DAYS);
+        Long totalToday = jdbcTemplate.queryForObject(
+                "SELECT count() FROM route_executions WHERE start_time >= ?",
+                Long.class, Timestamp.from(todayStart));
+
+        return new ExecutionStats(
+                current.totalCount, current.failedCount, current.avgDurationMs,
+                current.p99LatencyMs, current.activeCount,
+                totalToday != null ? totalToday : 0L,
+                prev.totalCount, prev.failedCount, prev.avgDurationMs, prev.p99LatencyMs);
     }
 
     @Override