feat(native): project foldable controls with SwiftUI

[rdlabo]

Summary

• Project foldable tabs, back navigation, menu buttons, and eligible fixed-toolbar actions from the Web fallback to a native SwiftUI adaptive surface when iOS exposes a physical side rail.
• Keep Ionic controls as the source of truth and forward native activation through the existing event, routing, and form-submit path.
• Clip and hit-test the hosting surface to the physical Duo rail so Web content remains visible and interactive elsewhere.
• Keep ion-menu, ion-modal, and ion-popover as independent surfaces.
• Retain the Web projection on Web, Android, older iOS, older plugin versions, and supported iOS devices without a foldable rail.

Transition and ownership

• Capture each toolbar control's foldable placement per routed-page epoch, and prehide rail-owned sources before Ionic's first transition paint. Text-only or opted-out controls stay on Web.
• Disable Ionic's fixed back-button clone animation on foldable pages through the shared transition's optional predicate, for both Web and native projection. Ordinary iPhone transitions are unchanged.
• Hand off suspension after the active projection retires, and resume prehide only after projection returns. Destroyed shells cannot be revived by stale suspension leases.
• Ignore the Web projection observer's own marker and ARIA mutations while retaining content, class, and DOM updates.
• The foldable-rail placement hint is optional and backward-compatible. SwiftUI owns adaptive placement and Liquid Glass; Ionic owns labels, icons, disabled and selected state, actions, and navigation.

Stack

1. feat: support iPhone Duo with vertical bars #213 — Web-first foldable layout and controls
2. This PR — Native-first SwiftUI ownership for controls relocated into the foldable rail
3. ionic-theme-utils#3 — shared transition opt-out, pinned until merged

Base: feat/foldable-toggle

Verification

• Theme TypeScript/CSS build and lint passed.
• 83 related Playwright E2E tests passed, including foldable handoff, back navigation, layouts, animations, and Native UI Shell.
• iPhone Duo iOS 27.1 simulator native rail UI test passed; transition video checked for the removed back-button clone.
• Shared utils: 16 unit tests, build, lint, format, and CI passed.
• Self, senior, independent acceptance, and OSS review cycles completed with no remaining findings.

[devin-ai-integration]

Devin Review found 3 potential issues.

[rdlabo]

Review cycle completed.

• Self-review: confirmed the tests are split by contract (DOM/native ownership, Swift state reconciliation, and real Duo interaction) without duplicating route screenshot coverage.
• Senior review: requested clearer ancestor/element opt-out and ordinary-fill ownership boundaries; fixed and re-reviewed to approval.
• Independent acceptance review: found the missing non-Duo capability boundary and combined status accounting. Added an explicit native foldableRail capability, retained Web projection when unavailable, preserved ordinary native controls, and fixed the public status aggregation. Re-reviewed to approval with no remaining findings.
• Validation: lint and TypeScript/CSS build passed; Native UI Shell Playwright suite 69/69 passed; Swift package tests on iPhone Duo Simulator 23/23 passed.

The fallback test verifies native non-ownership, visible/operable Web back and tab controls, and the public projected-count contract. Commit: 69bdf05.