Rebuild prepared queries on Actionbase Query #490

Background

#467 retired the stored query entity and its CRUD API because prepared queries were going to be redefined on Actionbase Query, and #466 said that redesign would be tracked separately. It never was, so I'm opening this to track it.

What I want is a query whose steps are fixed and whose values are not: a caller sends values alone, and whatever is derived from the body — a transform's compiled plan above all — is built once and reused. That only pays off if the registered body never changes between calls, so where the values go is most of the design.

Task

• Take transform and {name} binding on Actionbase Query
  • Reshape a query's results with SQL, in process (Step 1 of #490) #499
• Add the prepared-query API skeleton — endpoints, payloads, service declaration
  • Add the prepared-query API skeleton (Step 2 of #490) #491
• Store registered queries and the names pointing at them
• Serve registration, reads, and execution by id or by name
• Run an unregistered body with values sent alongside it (POST /graph/v3/query)
  • Register a query and call it by id or by name (Steps 3, 4 and 5 of #490) #500

Done When

A query is registered once and called by a name with values alone, and the transform's plan is compiled on the first call rather than on each one. I can edit a registered query, or move a name onto a different one, without resending the parts that did not change.

Notes

Two things need deciding, and neither belongs in a PR review.

Storage costs two system labels — one for queries, one for the names. #467 narrowed the metastore surface and #347's production run is still pending, so I'd want the owner of #347 to agree before this lands.

A name resolves through a cache held for metastoreReloadInterval, so after I move a name, instances disagree for up to a minute. That's the same bargain the label registry makes. If repointing a name is meant to be an incident response, a minute is too long, and the alternative is the metadata sync already used for labels.

One thing to record while I'm here: ActionbaseQuery.stats is declared but the v3 execution path ignores it. I store it and echo it back so nothing is silently dropped, but it does nothing yet.