New 'not fetched'/'no response' diagnostics for organization policy retrieval

Diagnostics gain a new status entry explaining why organization policy couldn't be fetched, covering cases such as a third-party provider, a custom base URL, no auth, a missing OAuth inference scope, or a Pro/Max account. It also reports why a fetch attempt failed, distinguishing auth_failed (including HTTP 403 with proxy guidance), timeout, network_error, parse_failed, spurious_304, and request_failed (with specific guidance for HTTP 404, 304, and 407), and notes that the fetch is 'Retried hourly while Claude Code runs; restart to retry now.'