Compile Ai Config Rule

Compile a plain-English rule description into structured conditions (TOS-1287 Phase 3), for the caller to confirm before staging it.

Owner-gated the same as every other AI-config write surface, even though this endpoint writes nothing - it spends a real, funded AI call (rule_compile, tracked via TrackedAIClient) against this identity's configuration on every invocation. The compiled predicates still have to pass through PUT .../ai-config/rules (full routing_policy + model-binding validation) to actually be saved - this endpoint's own validation (same routing_policy predicate rules, applied via rule_authoring.compile_rule_text) exists so a bad compile is rejected here, at the point it was authored, not silently accepted and only caught later at save time.