Constant MIGRATION_V12

pub const MIGRATION_V12: &str = r#"
CREATE TABLE IF NOT EXISTS event_queue (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    envelope_json TEXT NOT NULL
);
CREATE INDEX IF NOT EXISTS idx_event_queue_id ON event_queue(id);
DROP TABLE IF EXISTS paywall_events;

UPDATE schema_meta SET version = 12;
"#;

Repairs the chain after MIGRATION_V11 was edited in place (b35f9bcb5): it first shipped creating paywall_events, and a store that reached v11 then never runs the renamed text, so it has no event_queue and drops every funnel event. Idempotent on purpose — a store migrated after the edit already has event_queue (with queued events to keep). The paywall rail is gone and nothing drains paywall_events, so it is dropped. Never edit a migration that has shipped; append one like this.