task(deps): migrate to the standalone material_ui and cupertino_ui packages #8916

Context

Material and Cupertino are no longer part of the Flutter framework. They now ship as the pub packages material_ui and cupertino_ui, maintained in flutter/packages.

package:flutter/material.dart still exists in Flutter 3.47.2, so this is available rather than forced — the app builds and the full suite passes without it. But the framework copy is the legacy path now, and the longer we sit on it the more third-party packages move across underneath us.

Deliberately kept out of the Flutter 3.47.2 bump (#8915) to keep that PR reviewable: the bump is 405 files, this would add roughly 1350 more and mix a framework migration into a toolchain change.

Why this is not the one command the README implies

The material_ui README presents step 1 as dart fix --apply --code=migrate_design_widgets. That part is real and it works — but measured against this repo, two of the three README steps also apply, and there is a fourth thing the README cannot know about.

Step 1 — imports. 1346 files under mobile/ import package:flutter/material.dart; the fix proposes 1342 changes. Mechanical, but it is the whole app plus every package.

Step 2 — localizations. Applies here. GlobalMaterialLocalizations is referenced in 9 places, including the generated lib/l10n/generated/app_localizations.dart and divine_ui. Those classes move to material_ui / cupertino_ui.

Step 3 — compatibility bridge. Applies here. Third-party packages that still import package:flutter/material.dart need MaterialUiCompatibilityBridge wired through MaterialApp.builder so ThemeData and MaterialLocalizations resolve inside modern widget trees. pro_video_editor alone has 234 such files. This touches app bootstrap, so it wants its own thought rather than a find-and-replace.

Step 4 — our own guards. Not in the README. Several ratchet detectors are Dart AST passes keyed on the MaterialApp / CupertinoApp / WidgetsApp types — check_l10n_delegates_ceiling.sh and the design-system ceilings (check_raw_dialog_ceiling.sh, check_material_button_ceiling.sh). Once those types resolve to material_ui, an unchanged detector matches nothing and silently reports a clean file. Every guard that names a Material type has to be re-pointed, and its pinned test in mobile/test/tools/ updated with it.

Notes for whoever picks this up

• The fix data ships with the material_ui package, not the Flutter SDK. Grepping the SDK for migrate_design_widgets finds nothing, which makes the code look nonexistent — it is discovered once material_ui is a dependency.
• material_ui 1.1.1 declares flutter: ">=3.44.0", so it is compatible with our pin either way.
• divine_ui gates at 100% coverage and is one of the migrated packages, so its own suite moves with it.
• Worth splitting the mechanical import rewrite into its own commit, the way chore(deps): upgrade to Flutter 3.47.2 and drop the freezed models it breaks #8915 isolated the formatter churn, so review can skip it and focus on steps 2–4.

Done when

• The app and every package under mobile/packages/ build against material_ui / cupertino_ui
• Localization delegates come from the new packages and the l10n suite passes
• Third-party consumers still on package:flutter/material.dart render correctly through the bridge
• Every AST detector that names a Material type has been re-pointed, with its pinned test updated
• Full Mobile CI green, and a device smoke test on a real Samsung Galaxy covering camera, recording, upload and feed playback