pgAdmin 4: Local file inclusion and server-side request forgery in LLM API configuration endpoints

Local file inclusion (LFI) and server-side request forgery (SSRF) vulnerabilities in pgAdmin 4 LLM API configuration endpoints. User-supplied api_key_file and api_url preferences were passed to the LLM provider clients without validation. An authenticated user could read arbitrary server-side files by pointing api_key_file at any path readable by the pgAdmin process, or coerce pgAdmin into making requests to internal targets (e.g. cloud metadata services such as 169.254.169.254) by setting api_url, exploiting the chat path and model-list endpoints. Fix restricts api_key_file to the user's private storage (server mode) or home directory (desktop mode), enforces a printable-ASCII key shape and a 1024-byte read cap, and gates api_url against a configurable allow-list (config.ALLOWED_LLM_API_URLS) at every entry point. This issue affects pgAdmin 4: before 9.15.