protocol: multi-datasource config pattern for apps using ledger+work+qhorus together

[mdproctor]

Rule to formalise

Any casehub application that includes all three foundation extensions (casehub-ledger, casehub-work, casehub-qhorus) must configure two Hibernate persistence units:

PU	Datasource	Packages
default	default datasource	io.casehub.work.runtime.model + app domain
qhorus	qhorus named datasource	io.casehub.qhorus.runtime + io.casehub.ledger.runtime.model + io.casehub.ledger.model

Plus casehub.ledger.datasource=qhorus to route the ledger CDI producer to the qhorus PU.

Why: casehub-work expects @Default EntityManager. casehub-qhorus always runs on a named qhorus datasource (platform convention). casehub-ledger's producer selects by datasource name — when blank, it selects @Default. The only working split puts ledger on the qhorus PU (following claudony's pattern) while leaving work on the default PU.

Reference: discovered while bootstrapping casehub-aml (casehubio/aml#12). Pattern validated from claudony's application.properties.

Requested action

Add a protocol entry to docs/protocols/ covering this config pattern.