Add GutenbergKit opt-in announcement and per-site override

[jkmassel]

Adds a per-site GutenbergKit opt-in surfaced as a one-time bottom sheet on the My Site screen, with a matching toggle in Site Settings. The remote gutenberg_kit flag only gates the announcement / Settings toggle visibility — it is deliberately not part of editor routing.

Summary

• Show / defer / activate decisions live in GutenbergKitAnnouncementController — pure logic, unit-tested via an injected java.time.Clock.
• The per-site override is the single source of truth: presence (either direction) means the user has decided for that site; absence means we may prompt. No global opt-in flag, no separate "shown" flag.
• Maybe later writes a per-site GUTENBERG_KIT_ANNOUNCEMENT_DEFERRED_UNTIL_<url> 7 days out instead of locking in an opt-out. Swipe / back / tap-outside is treated as an implicit Maybe later so the sheet doesn't re-prompt on every My Site resume.
• Editor routing in GutenbergKitFeatureChecker is siteOverride ?: experimentalFlag && !disableKillSwitch. The remote gutenberg_kit feature flag is intentionally not in this expression — it only gates announcement / Settings toggle visibility. This lets us roll the announcement to a percentage of users without simultaneously flipping the default editor. When we're ready to make GutenbergKit the default for everyone, the change is a one-line edit (hard-code the fallback to true).
• Site Settings Try the new editor toggle: visible while the remote flag is on; checked state mirrors GutenbergKitFeatureChecker.isGutenbergKitEnabled(site) so it always reflects what the editor will actually do; on Aztec-default sites the row is shown disabled with an explanatory summary so users can still discover the option without a silent bundle-flip of mobileEditor.

Changes

• GutenbergKitAnnouncementController.kt (new): shouldShowAnnouncement(site), onActivate(site), setOverride(site, enabled), onMaybeLater(site). setOverride always clears any deferral, so "explicit decision supersedes a pending defer" lives in one place.
• GutenbergKitFeatureChecker.kt: editor-routing resolution drops the remote flag from the OR; only siteOverride and experimentalFlag decide, with the kill switch winning over both. Field isGutenbergKitFeatureEnabled on FeatureState is kept for logging / informational purposes only.
• MySiteViewModel.kt / MySiteFragment.kt: announcement check moved to My Site onResume(). Posts _onShowGutenbergKitAnnouncement: SingleLiveEvent<Event<SiteModel>>. Fragment observer guards with isStateSaved and an already-attached-instance check before .show().
• GutenbergKitAnnouncementBottomSheetFragment.kt: @AndroidEntryPoint, Hilt-injected controller, takes a SiteModel via newInstance(site). Activate / Maybe later / dismiss-without-decision all route through the controller. Insets only consume Type.statusBars() so IME / gesture / bottom-bar insets still propagate. "Learn more" uses a %1$s placeholder so translators can position it anywhere in the body.
• SiteSettingsFragment.java: new mGutenbergKitPref row. refreshGutenbergKitToggleAvailability() is called from both initPreferences() and setPreferencesFromSiteSettings(), so flipping "Use block editor as default for new posts" on the same screen re-enables the GBKit row without leaving Settings. Toggle writes go through mGutenbergKitAnnouncementController.setOverride(...).
• AppPrefs.java: GUTENBERG_KIT_OPT_IN_SITES / OPT_OUT_SITES (deletable StringSets) and per-site GUTENBERG_KIT_ANNOUNCEMENT_DEFERRED_UNTIL_<url> longs. The previous draft's GUTENBERG_KIT_USER_OPT_IN and GUTENBERG_KIT_ANNOUNCEMENT_SHOWN undeletable flags are removed — there's no longer any state that should survive logout.
• EditorLauncher.kt: logFeatureDisabledReason and getFeatureFlagsString updated to reflect the new resolution (mentions site override, no longer claims the remote flag enables routing).
• EditorCapabilityResolver.kt: passes site through the GBKit gate so Theme Styles and Third-Party Blocks resolve against the same per-site view the launcher uses.
• RELEASE-NOTES.txt: entry under 26.8.

Test plan

• Fresh install, remote flag on, site defaults to block editor:
  • Open the app → My Site → announcement appears.
  • Tap Activate → sheet dismisses → creating a new post on that site opens GutenbergKit. Returning to My Site, the sheet does not reappear.
  • Tap Maybe later → sheet dismisses → does not reappear within the 7-day window. Verify reappearance after expiry by shortening DEFER_DURATION_MILLIS locally (or jumping the device clock).
  • Swipe down / tap outside / back-button dismiss behaves the same as Maybe later (no reappearance for 7 days).
• Remote flag on, no per-site opt-in, no experimental flag:
  • Creating a new post opens Aztec / legacy editor, not GutenbergKit. (Verifies the remote flag no longer gates editor routing.)
• Aztec-default site (mobileEditor == "aztec"):
  • Announcement does not appear on My Site.
  • Site Settings shows "Try the new editor" disabled, with summary including "Switch to the block editor first…".
  • Toggling Use block editor as default for new posts ON → after the settings refresh, "Try the new editor" re-enables in place without leaving the screen.
• Site Settings Try the new editor toggle:
  • Toggle ON → that site opens GutenbergKit; other sites are unaffected.
  • Toggle OFF after opting in → that site opens Aztec.
  • After Maybe later on the sheet, toggling the Site Settings switch (either direction) clears the deferral.
• Remote flag off:
  • Announcement does not appear.
  • "Try the new editor" row is hidden in Site Settings.
• Configuration change: rotate the device while the sheet is open → sheet recreates without writing a deferral.
• Unit tests: GutenbergKitAnnouncementControllerTest, GutenbergKitFeatureCheckerTest, EditorCapabilityResolverTest, MySiteViewModelTest pass.

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🤖 Build Failure Analysis

This build has failures. Claude has analyzed them - check the build annotations for details.

[codecov]

Codecov Report

❌ Patch coverage is 39.77273% with 53 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.34%. Comparing base (96fc478) to head (2bfdd30).

Files with missing lines	Patch %	Lines
.../java/org/wordpress/android/ui/prefs/AppPrefs.java	0.00%	38 Missing ⚠️
...a/org/wordpress/android/ui/posts/EditorLauncher.kt	0.00%	8 Missing ⚠️
.../org/wordpress/android/ui/prefs/AppPrefsWrapper.kt	0.00%	4 Missing ⚠️
...ess/android/ui/posts/GutenbergKitFeatureChecker.kt	81.81%	1 Missing and 1 partial ⚠️
...org/wordpress/android/ui/mysite/MySiteViewModel.kt	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk   #22813      +/-   ##
==========================================
- Coverage   37.34%   37.34%   -0.01%     
==========================================
  Files        2320     2321       +1     
  Lines      124653   124728      +75     
  Branches    16941    16962      +21     
==========================================
+ Hits        46549    46576      +27     
- Misses      74339    74385      +46     
- Partials     3765     3767       +2     

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