Run SQLx migrations on startup

migrations/20240101000003_create_user_activity.sql

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+-- Create user_activity table
+CREATE TABLE IF NOT EXISTS user_activity (
+    id SERIAL PRIMARY KEY,
+    "user" INTEGER NOT NULL UNIQUE,
+    updated TIMESTAMP WITHOUT TIME ZONE NOT NULL
+);
+
+-- Create unique index on user (if not exists from UNIQUE constraint)
+CREATE UNIQUE INDEX IF NOT EXISTS user_activity_user_key ON user_activity("user");
+
+-- Add foreign key constraint if it doesn't exist
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint
+        WHERE conname = 'fk_user_activity_user_settings_id_user'
+    ) THEN
+        ALTER TABLE user_activity
+        ADD CONSTRAINT fk_user_activity_user_settings_id_user
+        FOREIGN KEY ("user") REFERENCES user_settings(id);
+    END IF;
+END $$;