do sessions in memory and also fix glaring security hole

Femto.Database/Migrations/20250529101346_SessionsRework.sql

@@ -0,0 +1,13 @@
+-- Migration: addLongTermSessions
+-- Created at: 29/05/2025 10:13:46
+
+DROP TABLE authn.user_session;
+
+CREATE TABLE authn.long_term_session
+(
+    id              serial PRIMARY KEY,
+    selector        varchar(16) NOT NULL,
+    hashed_verifier bytea       NOT NULL,
+    expires         timestamptz not null,
+    user_id         uuid REFERENCES authn.user_identity (id)
+);