Rule compiler, positive fragment: persistent rules as arrangements in the maintainer (V3) #310

Part of epic #305.

Problem. Rules are compiled per query into fresh dataflows and their results discarded (src/lib.rs:1543-1775, src/code_generator/mod.rs:378-440); the only compiled-rule type is never executed (src/derived_relations.rs:50-70).

Target. Compile the catalog's rules (select/project/join/union, arithmetic, comparisons, pure string/vector functions; no recursion/negation/aggregates yet, which are refused by the maintainer until V4/V5 and served by the recompute path meanwhile) from the canonical IR into the maintainer: scans import base/view arrangements, joins use join_core on arranged inputs, each head gets arrange_by_key (first column) and arrange_by_self. Build at registration from current arrangements; drop at removal. The query path still recomputes (V9 flips reads). Tests reuse the existing codegen closures where possible so operator semantics are shared.

Acceptance. Oracle on random histories: every maintained view equals recompute at every revision for a corpus of non-recursive rule packs (shop pack, voice pack minus recursion); an ordinary update does not rebuild the dataflow (counter); maintenance time per commit and bytes per view reported; rule_evaluations unchanged (reads still recompute).

Size L (split allowed: single rule / multi-rule stratified). Dependencies V2. Order slot 2. Supersedes #181.