feat(asapquery): gate warm routes on materialization readiness

[zzylol]

Summary

• track materializing, ready, and serving state per materialization and physical-plan generation
• require complete and fresh closed-window coverage before a QueryPlan route returns a warm result
• convert incomplete, missing, or generation-raced coverage into an explicit capability miss for Prometheus fallback
• expose materialization phase and coverage through the physical-plan status endpoint

Stack

• depends on feat(asapquery): compile startup workloads into physical plans #496

Verification

• cargo test -p data_plane query_engines::asap_query_engine::engine --lib
• cargo test -p data_plane storage_engines::types::hot_reload_config::tests --lib
• cargo test -p control_plane query_plan

This PR is intentionally open and should be reviewed/merged after its stack parent.