Collection Filter Authoring

Build a nested datasource filter contract, connect it to the consumer, and verify that the requested Any/All semantics actually execute. Use the contract reference for persisted trees, generated column constants, grid modes, and empty collections.

The #296 interface is implemented; see verification evidence and remaining live checks. Both generate and generate-flow support explicit dotted paths and the collection opt-in below. CLI 0.5.9 ships them (verified live). On 0.5.8, check dxs datasource generate --help: that version number alone does not distinguish builds before and after the merge.

Workflow