Freeze settled weekly facts

[mixn1998]

What changed

• freeze weekly plan totals, completion totals, and overdue items at weekly settlement
• keep current-week overdue content live while settled weeks remain immutable
• make monthly week cards read frozen weekly/daily facts
• constrain weekly AI harvests to the exact completed count
• migrate historical SQLite snapshots safely after event replay
• include the existing local-service startup hardening commit

Why

Historical weekly statistics and overdue content were being recalculated from mutable plans, so later rescheduling or sync changes could rewrite settled weeks. The AI harvest also inferred the completion count from content and produced an incorrect number.

Validation

• npm.cmd test — 168 tests passed
• npm.cmd run typecheck
• npm.cmd run build
• live local state migrated to schema 22 with the settled 2026-07-20—2026-07-26 week frozen at 41/41