Affected: npm: @openhop/server

## Path Traversal in Flow ID File Operations

### Summary

`@openhop/server` passes unsanitized HTTP route parameters directly to `path.join()` when constructing filesystem paths for flow YAML files. An unauthenticated attacker who can reach the server can read arbitrary `.yaml` files accessible to the OpenHop process outside the configured flow directory, and can delete arbitrary `.yaml` files at any path reachable by the process. Because CORS is set to `origin: true` (allow all origins), a victim's browser can be used to exploit the vulnerability against a loopback-bound instance. Docker deployments bind `HOST=0.0.0.0` by default, enabling direct remote exploitation. CVSS Base Score: **8.3 (High)**.

### Details

`FlowStore.filePath()` in `packages/server/src/store.ts:52–53` constructs a filesystem path by concatenating the caller-supplied `id` directly into `path.join`:

```ts // packages/server/src/store.ts:52-53 private filePath(id: string): string { return join(this.dir, `${id}.yaml`) } ```

This result is consumed by two sinks:

- **Read** (`packages/server/src/store.ts:78`): `readFile(this.filePath(id), 'utf-8')` - **Delete** (`packages/server/src/store.ts:105`): `unlink(this.filePath(id))`

The `id` value originates from unauthenticated Fastify HTTP route parameters:

- `GET /api/flows/:id` (`packages/server/src/routes.ts:306`) → `store.get(id)` at line 333–335 - `DELETE /api/flows/:id` (`packages/server/src/routes.ts:509`) → `store.delete(id)` at line 539–541

Th…