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/component/src/ui/modal/prompt-modal.tsx

@@ -12,12 +12,16 @@ import {
 import type { ButtonProps } from '../button';
 import { Button } from '../button';
 import Input, { type InputProps } from '../input';
+import { ModalConfigContext } from './context';
 import type { ModalProps } from './modal';
 import { Modal } from './modal';
 import { desktopStyles, mobileStyles } from './prompt-modal.css';
 
 const styles = BUILD_CONFIG.isMobileEdition ? mobileStyles : desktopStyles;
 
+const getCssLength = (value: string | number) =>
+  typeof value === 'number' ? `${value}px` : value;
+
 export interface PromptModalProps extends ModalProps {
   confirmButtonOptions?: Omit<ButtonProps, 'children'>;
   onConfirm?: ((text: string) => void) | ((text: string) => Promise<void>);
@@ -57,8 +61,10 @@ export const PromptModal = ({
   autoFocusConfirm = true,
   headerClassName,
   descriptionClassName,
+  contentOptions,
   ...props
 }: PromptModalProps) => {
+  const { dynamicKeyboardHeight } = useContext(ModalConfigContext);
   const [value, setValue] = useState(defaultValue ?? '');
   const onConfirmClick = useCallback(() => {
     Promise.resolve(onConfirm?.(value))
@@ -88,8 +94,21 @@ export const PromptModal = ({
     <Modal
       preserveEditingFocusOnAction={BUILD_CONFIG.isMobileEdition}
       contentOptions={{
-        className: styles.container,
+        ...contentOptions,
+        className: clsx(styles.container, contentOptions?.className),
+        style: {
+          ...contentOptions?.style,
+          ...(BUILD_CONFIG.isMobileEdition
+            ? {
+                maxHeight: dynamicKeyboardHeight
+                  ? `calc(100dvh - ${getCssLength(dynamicKeyboardHeight)} - 32px)`
+                  : 'calc(100dvh - 32px)',
+                overflowY: 'auto',
+              }
+            : null),
+        },
         onPointerDownOutside: e => {
+          contentOptions?.onPointerDownOutside?.(e);
           e.stopPropagation();
           onCancel?.();
         },