Finds and returns the portfolio companies listed on a VC or investment fund's website. Use this skill when the user says things like "look up portfolio of [fund]", "get portfolio companies for [fund website]", "what companies does [fund] invest in", "find portfolio page for [url]", "list investments of [fund]", or "/lookup-fund-portfolio". Input: fund website URL or domain. Output: structured JSON list of portfolio company names. Saves the result locally at ~/.carta-crm/fund-portfolios/ for auditing.