Queries read deployed views from arrangements; revision on query replies (V9) #315

Part of epic #305.

Problem. combine prepends the dependency closure's rules to every query and the engine re-derives them (src/storage_engine/snapshot.rs:302-405); a one-row bound read costs 62 ms / 2.9 s at 1M edges and depends on the rule's recursion form (report 4.1, A.4); base point reads stream the whole relation (?edge(K,Y) 5.4 ms at 1M; src/code_generator/mod.rs:1514-1523).

Target. With engine.views = maintained: query workers import the maintainer's base and view arrangements at the frontier (import_frontier) into the query's short-lived dataflow; deployed heads are bound to imported arrangements instead of rules; a query whose body is one deployed atom with leading key columns bound is served by a cursor seek without a dataflow; ?base(K,..) uses the keyed base arrangement; session rules compile on top; sort/limit/offset unchanged; query replies carry revision. Guard queries of guarded writes use the same path at the staging revision.

Acceptance. rule_evaluations = 0 and view_reads > 0 for every read of a deployed view (fixture corpus + snapshot specs); results equal recompute at the same revision (oracle); B1-B4 pass (bound view read <= 1 ms, base point read <= 1 ms at 1M edges); recursion form no longer changes bound-read cost; queries never run on the maintainer thread (thread assertion).

Size L. Dependencies V5, #296 merged. Order slot 4. Supersedes #187 (serving half).

Scenarios. flips scenario S2 to required (counter part, reads::s2_one_row_view_read_is_a_lookup); flips scenario S3 to required (counter part, reads::s3_ad_hoc_query_joins_facts_and_views); flips scenario S4 to required for the query revision (consistency::s4_subscription_and_query_agree_at_a_revision). Their expected failures name #315 (#337).