Persist exact-microsecond quota observations and inert exclusions

[acgxv]

Summary

• persist exact-microsecond five-hour and seven-day quota observations
• add inert account/window exclusion transactions with durable idempotent receipts
• fail closed on malformed, stale, ambiguous, or low-confidence quota facts

Migration

• breaking V8 pre-release schema transition; populated V7 quota state requires disposable-database recreation

Verification

• fresh exact-candidate reviewer verdict: APPROVED/READY
• owner validation: 24 Rust tests, PostgreSQL 18 harness 38/38, architecture/gate/audit tests, strict Clippy, pinned rustfmt, and diff check
• Manager independently verified signed commit 3eec9e5 and exact 14-file frozen tree

Linear: XY-1274