Unified nudge framework

[adibarra]

A single registry-driven system for in-app engagement nudges (banners, modals, and toasts) that replaces the handful of one-off implementations currently scattered across the app.

Requirements

• Each nudge declares its trigger, audience/conditions, dismissal behavior, and persistence (e.g. dismissed-forever vs. session-only) in the registry.
• Migrate every existing engagement-style one-off onto the new framework and delete the old implementations. No parallel systems left in the codebase when this lands.
• Dismissal state for "don't show again" nudges persists across sessions per user/browser, some of them have a mechanic to show nudges again after some time which we need to keep.
• Analytics events for nudge shown, dismissed, and primary-action clicked, with the nudge id as a property.
• Tests covering trigger conditions, dismissal persistence, and that each migrated nudge still fires in the same situations as before.
• The unoffical runs banner works very differently from the other nudges, up to you if you want to keep that one separate or unify it.

Nice to have

• Scheduling support (show after date X, hide after date Y) so time-bound campaigns don't need code changes to retire.
• There is a stale PR for banner announcements which you may be interested in integrating (feat: add automated announcement banner for new benchmark data #174).