fix(query-engine): services filter sidebar now includes all signal types

[robbiemu]

Fixes #285

Problem

The /services page filter sidebar only showed services that have traces (via service_overview_spans / service_overview_hourly). Services that only send logs or metrics were missing from the filter dropdown.

Solution

Modified servicesFacetsQuery() in packages/query-engine/src/ch/queries/services.ts to union service names from all signal tables:

1. Traces: service_overview_spans (existing)
2. Logs: logs_aggregates_hourly (new)
3. Metrics: metrics_gauge, metrics_sum, metrics_histogram, metric_catalog (new)
4. Aggregated rollup: service_usage (new)

Each branch uses the appropriate table and where conditions for its signal type, following the same UNION ALL pattern as the existing code.

Testing

• All 16 services tests pass
• All 647 query-engine tests pass
• Typecheck passes

Design Notes

• The Services page is a cross-signal overview — its filter should show all services regardless of signal type
• Signal-specific pages (/traces, /logs, /metrics) continue to use their own signal-specific facet queries
• This preserves the existing per-signal filter behavior while fixing the cross-signal overview

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