feat(mcp): service_deployments, route_usage, ingest_freshness, db_query_volume and ingest_usage - #1233

🟡 Confidence 3/5 · needs attention
_{quality 100/100 · no findings · tests partial · risk medium · 5/5 new units observable}

Adds five read-only MCP tools (service_deployments, route_usage, ingest_freshness, db_query_volume, ingest_usage) with the query builders, output schemas and benchmark fixtures behind them. All are tenant-scoped and read existing rollups, so the change is safe to merge. The new test file was not read before the pass ended.

• serviceDeploymentsQuery ranks versions per (service, environment) with row_number() before the global limit
• routeUsageQuery splices raw, minutely and hourly operations tiers into METHOD /route usage
• ingestFreshnessQuery/logsFreshnessQuery probe newest signal timestamps, traces from service_operations_minutely
• dbQueryVolumeQuery unions the query-shape rollup with a raw edge mirroring its write filter

_{e700b5f · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}