fix(migrations): create sign_sessions table before altering it

The catch-up migration assumed sign_sessions already existed, but
databases created from older schema dumps may not have this table.
Adding CREATE TABLE IF NOT EXISTS prevents the migration from failing
with "relation does not exist" on those databases.

server/migrations/sql/0002_catch_up_patches.sql

@@ -17,6 +17,15 @@
 ------------------------------------------------------------------------
 -- Patch 00: psn-id (sign_sessions primary key + psn columns)
 ------------------------------------------------------------------------
+CREATE TABLE IF NOT EXISTS public.sign_sessions (
+    id SERIAL PRIMARY KEY,
+    user_id integer,
+    char_id integer NOT NULL DEFAULT 0,
+    token character varying(16) NOT NULL,
+    server_id integer,
+    psn_id text
+);
+
 ALTER TABLE users ADD COLUMN IF NOT EXISTS psn_id TEXT;
 
 DO $$ BEGIN