UX Validate

Trigger whenever reviewing a PR, code change, or feature for shipping readiness and a UX Discovery Document exists at docs/ux-discovery/ — always invoke on phrases like "review this PR before we ship", "is this feature ready to ship", "validate this implementation against our discovery doc", "check that this code matches what we researched", "before we mark this complete sanity check it", "does this still serve the primary persona", "we're about to ship is anything missing", "review the implementation for UX alignment", "I'm worried we drifted from the original user goals", or "the team wants to ship it but I'm not sure". This is the throughout companion to ux-discover: it runs DURING and AFTER implementation to catch drift between what was researched and what's being shipped, scoring persona alignment, JTBD coverage, journey gap closure, design-principle adherence, telemetry instrumentation, and assumption validity against the discovery doc. It is COMPLEMENTARY to code review, NOT a replacement — run it alongside superpowers:code-reviewer, linters, and generic code-quality reviewers; both dimensions should gate the same PR. Push to invoke even when the user only asks for a "quick sanity check" or "is this good to merge" on any user-facing surface with a discovery doc present. Do NOT trigger when no docs/ux-discovery/ document exists (run ux-discover first), for pure technical refactors with no user-facing surface, engineering-internal bug fixes, performance or security reviews, dependency upgrades, doc generation, or while ux-discover is still in progress.