feat: add audit_log table migration

internal/database/migrations/023_add_audit_log.sql

@@ -0,0 +1,18 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS audit_log (
+    id TEXT PRIMARY KEY,
+    occurred_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    user_id TEXT REFERENCES user(id) ON DELETE SET NULL,
+    action TEXT NOT NULL,
+    resource_type TEXT,
+    resource_id TEXT,
+    ip TEXT,
+    user_agent TEXT,
+    metadata_json TEXT
+);
+
+CREATE INDEX IF NOT EXISTS idx_audit_log_user_id_occurred_at ON audit_log(user_id, occurred_at DESC);
+CREATE INDEX IF NOT EXISTS idx_audit_log_action_occurred_at ON audit_log(action, occurred_at DESC);
+
+-- +goose Down
+DROP TABLE IF EXISTS audit_log;