remove preact and create setup wizard

apps/server/internal/database/migrations/000011_instance_settings.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS instance_settings;

apps/server/internal/database/migrations/000011_instance_settings.up.sql

@@ -0,0 +1,13 @@
+CREATE TABLE IF NOT EXISTS instance_settings (
+    id INTEGER PRIMARY KEY CHECK(id = 1),
+    setup_completed_at TEXT,
+    signups_enabled INTEGER NOT NULL DEFAULT 0 CHECK(signups_enabled IN (0, 1)),
+    updated_at TEXT NOT NULL
+);
+
+INSERT OR IGNORE INTO instance_settings (id, setup_completed_at, signups_enabled, updated_at)
+SELECT
+    1,
+    CASE WHEN EXISTS(SELECT 1 FROM users) THEN datetime('now') ELSE NULL END,
+    CASE WHEN EXISTS(SELECT 1 FROM users) THEN 1 ELSE 0 END,
+    datetime('now');