first commit

internal/db/migrations/0002_idempotent_target.sql

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+-- target_expires_at captures the expiry value computed at first confirmation
+-- attempt. Subsequent attempts (e.g. after a crash mid-confirm) read this
+-- value back so user mutation stays idempotent.
+ALTER TABLE pending_invoices ADD COLUMN target_expires_at TEXT;
+
+CREATE INDEX idx_audit_pubkey ON audit_log(pubkey);
+CREATE INDEX idx_audit_created ON audit_log(created_at);
+CREATE INDEX idx_webhook_outbox_status ON webhook_outbox(status, created_at);
+CREATE INDEX idx_dm_outbox_status ON dm_outbox(status, created_at);