Beta freeze

Last feature change before launch. We pulled the muting controls users had been asking for, wired up the welcome email so new accounts do not arrive in an empty room, and gave the admin queues real search so we can actually find a stuck post when we need to.

Added

• Notification preferences -- mute by category (schedules, failures, referrals, billing) from one settings page.
• Welcome email drip -- a five-message Resend sequence that walks new accounts through connecting a channel, scheduling a first post, and unlocking analytics.
• Search and filter on admin queues -- find any post or job by user, status, channel, or date range without scrolling.