feat(ios): polish onboarding and native sign-in flow (#15217)

## Summary
- Reworks the iOS onboarding, native sign-in, and paywall flow so
first-install and cold-start entry stay native, adaptive, and aligned
with the current login/subscription gates.
- Removes onboarding swipe paging, refines onboarding/paywall layout
behavior, and keeps AI/paywall entry behavior consistent for logged-in
and subscribed users.
- Adds the new mobile all-docs empty states with localized copy and
dialog entry points, and closes the remaining review follow-ups by
removing the onboarding plan artifact and dropping the iOS AI
subscription bypass.

## Test plan
- Built the iOS app for simulator with `xcodebuild -workspace
App.xcworkspace -scheme App -configuration Debug -sdk iphonesimulator
-destination 'generic/platform=iOS Simulator' ARCHS=arm64
ONLY_ACTIVE_ARCH=YES CODE_SIGNING_ALLOWED=NO CODE_SIGNING_REQUIRED=NO
build` during the native onboarding/sign-in flow work.
- Let the repo pre-commit hooks run on the latest follow-up commit
(`prettier` + `eslint --fix`).
- Checked diagnostics for the edited TS/TSX files after the review
follow-up changes.
- Manually iterated on onboarding/native sign-in/paywall UI states in
simulator during implementation.

---------

Co-authored-by: DarkSky <darksky2048@gmail.com>

packages/frontend/apps/ios/App/Podfile.lock

@@ -54,6 +54,6 @@ SPEC CHECKSUMS:
   CapacitorPluginAppTrackingTransparency: f0df8fe65d07d3854de3dad832caf192262bbaa5
   CryptoSwift: 967f37cea5a3294d9cce358f78861652155be483
 
-PODFILE CHECKSUM: ea5ce301a5d89089eaf7d25b0c1fd49293dcfc20
+PODFILE CHECKSUM: c36da240bb7ce656c8648d643cd942599f770b59
 
 COCOAPODS: 1.17.0