Reader: Harden the Skip button and add interest-selection debug controls - #25924

Follow-up to the Skip button (#25921, now merged): review fixes to the new Skip button, plus internal tooling to exercise the interest-selection screen.

What changed

Skip button (user-facing)

• Track a select_interests_skipped event. Tapping Skip completes the flow and permanently sets readerDidSelectInterestsKey, but emitted nothing — so the funnel couldn't tell a skip from an abandonment (select_interests_shown with no terminal event). Adds the event alongside the existing select_interests_shown / select_interests_picked.
• Debounce the Skip button. The primary save path disables its button and fades the content before dismissing; Skip did neither, so a fast double-tap during the ~0.35s dismiss animation could re-enter ReaderDiscoverViewController.didSaveInterests() — a second dismiss and another forced stream refresh. sender.isEnabled = false on first tap prevents the re-entry.
• Complete the flow on Skip. The save-success path calls readerDiscoverFlowDelegate?.didCompleteReaderDiscoverFlow(); Skip didn't. This is inert today — the only flow that shows Skip (.discover) never sets the delegate, and the only flow that sets the delegate (Stats' "Grow your audience" nudge) uses a config with showsSkipButton == false. But those two config flags are independent: flip showsSkipButton on the Stats config and Skip would silently fail to mark the nudge complete, so the card would reappear on every visit. Calling the delegate on Skip closes that with no change to current behavior.

Debug controls (internal builds only)

The select-interests screen is a one-time onboarding prompt, hard to see again during development. Adds two actions under Developer → Settings:

• Show Reader Interests Screen — presents the .discover screen (with the Skip button) directly, bypassing both the readerDidSelectInterestsKey flag and the isFollowingInterests check that gate it, so it works on any account.
• Reset Reader Interests Prompt — clears readerDidSelectInterestsKey so the real auto-prompt fires again on the next Reader → Discover visit (still subject to isFollowingInterests — an account following no tags).

The reset action posts a text confirmation notice. It first reused the debug menu's shared showSuccessNotice(), which posts a bare "✅"; app notices render on an inverted background (light in dark mode), so an emoji-only toast reads as a blank light box in dark mode. A text title renders legibly in both appearances.

Not in this PR — Skip is unavailable in the offline / empty state

When the interests request fails or returns empty, the Discover flow shows only the "Try Again" NoResults overlay: Skip — like the primary button — lives inside contentContainerView, which fades to alpha 0 during loading and is covered by the overlay, and the sheet is presented without a nav bar and with isModalInPresentation = true, so there is no way out until the network recovers. This predates the Skip button (the primary button is equally unavailable there); fixing it means extending the deprecated NoResultsViewController or restructuring the empty/error presentation — both larger than a review follow-up and risky for the Stats flow that shares this screen.

Test plan

• Reader → Discover as an account that hasn't picked interests: tap Skip → the sheet dismisses, the stream refreshes, and the prompt doesn't return.
• A select_interests_skipped event fires on Skip (Tracks debug console); select_interests_picked still fires on the Done path.
• Double-tap Skip rapidly → one dismiss, no second stream refresh.
• VoiceOver reads the Skip button as "Skip, button".
• Developer → Settings → Show Reader Interests Screen presents the screen on an account that already follows tags.
• Developer → Settings → Reset Reader Interests Prompt shows a legible "Reader interests prompt reset" toast in dark mode (verified on an iPhone 15 Pro, iOS 27).

Related

• Follows Added the Skip Button to ReaderDiscoverViewController #25921 (merged)