Add a read-only `notification` (alias `n`) top-level command to view notification channels configured in the workspace. Supports all 12 provider types: discord, email, google_chat, grafana_oncall, ntfy, pagerduty, opsgenie, slack, sms, telegram, webhook, and whatsapp. - `notification list` shows ID, name, provider, and monitor count - `notification info <id>` shows full provider config, linked monitors, and timestamps with nested provider-specific data in JSON output - Follows the same patterns as status-page (dual client factory, interceptor test helpers, JSON/table output branching)