Remove the dead materialization machinery (V0) #307

Part of epic #305.

Problem. auto_materialize, refresh_materializations, evaluate_rule, materialize_derived_relation, set_auto_materialize (src/storage_engine/mod.rs:2342-2350,2483-2549), DerivedRelationsManager/CompiledRule (src/derived_relations.rs, 797 lines; clauses always empty per src/storage_engine/catalog_change.rs:424-429), the materialized_relations field threaded through snapshots and the change log (src/storage_engine/snapshot.rs:74,249,616-621; src/storage_engine/precondition.rs:131-135,173), install_catalog's dd.register_rule branch (catalog_change.rs:333-348), shadow_write (program_commit.rs:396-413) and materialize_tests.rs are reachable only from tests and describe a design that will not be built. They mislead readers (and the architecture doc) and add a lock around every snapshot publish when enabled.

Target. Delete all of the above and the IncrementalEngine derived-relations API (register_rule, set_materialized, notify_base_update, derived_relations()), keeping the worker-thread skeleton (IncrementalEngine::new/worker_loop/insert/delete, incremental.rs:95-330) as the seed of V2. publish_snapshot takes the simple branch only. Docs in src/ rewritten per D1.

Acceptance. grep -rn "materializ" src/ returns only comments explaining recompute-on-read; all tests pass; cargo clippy -D warnings clean; snapshot publish has no DerivedRelationsManager lock; binary size and test count reported in the PR.

Size M. Dependencies none. Order slot 1.