feat: add skimmers based on user job preferences

- in the settings, the user should be able to enter job titles that they prefer (e.g. UI/UX Designer, Software Engineer)
- based on a list of preferences (posting recency, location, etc.), openclaw should be able to search the web for similar jobs based on these titles.

Look at the settings module to understand how user preferences are stored. Examine the existing web search or scraping logic to see how job listings are fetched. The feature requires integrating user-entered job titles with search criteria like recency and location, and likely adding a new skimmer component. Check for any existing tests related to settings or job searches to understand the codebase structure.

索引モデルが issue の本文から書いたものです。