Support recursive stable pagination with max-depth

[theronic]

Summary

• replace recursive full-closure materialization with a stable discovery-order frontier cursor
• add :max-depth runtime guards with a default of 50
• keep acyclic lookups on the existing fast static merge path
• update recursive lookup/count semantics to exact deduplicated stable order instead of global eid order

Verification

• eacl.datomic.schema-test
• eacl.datomic.config-test
• eacl.datomic.parser_test
• eacl.datomic.impl.indexed-test
• eacl.spice-test
• non-recursive pagination benchmark remains within existing thresholds
• recursive pagination benchmark shows the regression is repaired by a wide margin

Notes

• recursive pagination order can change, but result membership remains exact and deduplicated
• this unblocks 0tx shared subtree access on the new EACL SHA