feat: Implement temporary API key based on system UUID for UI access

This commit introduces a new authentication mechanism for the web UI.
Instead of requiring a pre-configured API key, a temporary API key is
generated based on the system's UUID. This key is passed to the UI
as a URL parameter and used for API requests.

Changes:
- Added a new utility to get the system UUID and generate a temporary API key.
- Modified the `ccr ui` command to generate and pass the temporary API key.
- Updated the authentication middleware to validate the temporary API key.
- Adjusted the frontend to use the temporary API key from the URL.
- Added a dedicated endpoint to test API access without modifying data.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

ui/src/types.ts

@@ -40,3 +40,5 @@ export interface Config {
   API_TIMEOUT_MS: string;
   PROXY_URL: string;
 }
+
+export type AccessLevel = 'restricted' | 'full';