Recompute a ranking from a refresh message (Step 4 of #386)

[zipdoki]

Summary

The previous PR schedules a refresh for the instant a bucket leaves the sliding window, but nothing consumes it. A windowed ranking goes stale the moment its oldest bucket ages out, and stays stale. This consumes the refresh.

POST /aggregations/v1/sweep takes refresh messages and recomputes the ranking row each one names:

{
  "items": [
    {
      "type": "TOPK",
      "item": {
        "database": "graph", "table": "likes", "topk": "daily_likes",
        "source": "...", "target": "...", "direction": "OUT",
        "entity": "...", "topkDimensionValue": "...", "dimensionValues": "",
        "ranges": "", "properties": {}, "refreshAt": 1755500000000
      }
    }
  ]
}

{ "items": [ { "database": "graph", "table": "likes", "topk": "daily_likes", "entity": "...", "status": "OK", "error": null } ] }

SweepItem resolves item polymorphically off type through Jackson's EXTERNAL_PROPERTY, so a second aggregation kind adds a SweepItemPayload subtype and a JsonSubTypes entry rather than a second endpoint. AggregationHandler gains sweep, and AggregationService dispatches by AggregationType instead of fanning out to
every handler the way aggregate does — a refresh message already knows which kind it belongs to.

TopkSweepItem carries exactly what refreshKey encodes, plus refreshAt, so the consumer can rebuild the ranking without reading the queue row back.

Sweep is a write path and is rejected under read-only mode, alongside POST /aggregations/v1/aggregate.

Stacked on #494 — that needs to land first.

Part of #386.

Test plan

• ./gradlew :engine:test --tests '*TopkAggregationHandlerTest*' — recompute from a refresh message, including the rank row rewrite
• ./gradlew :engine:test --tests '*AggregationServiceTest*' — dispatch to the handler named by AggregationType
• ./gradlew :server:test --tests '*MetadataAggControllerE2ETest*' — POST /aggregations/v1/sweep over HTTP, per-item status and error
• ./gradlew :server:test --tests '*ReadOnlyRequestFilterTest*' — sweep is blocked in read-only mode
• ./gradlew spotlessKotlinCheck build — formatting and full build

AI Assistance

• This PR was written largely with AI assistance.
  • Tool / model: Claude Code (Opus 5)