epic(ui): migrate QueryaDropdown, QueryaModalDialog, and QueryaSearchField off shadcn_flutter to Flutter primitives #1365

Goal

Eliminate remaining shadcn_flutter dependencies inside the Querya UI Kit (lib/shared/widgets/) by migrating QueryaDropdown, QueryaModalDialog, QueryaSearchField, QueryaTabStrip, and QueryaSpinner to native Flutter primitives.

Context

While Epic #1331 targets migrating all buttons to the Querya UI Kit, 65 files across the project still import package:shadcn_flutter. Most notably, core widgets inside lib/shared/widgets/ still depend directly on shadcn_flutter types:

• querya_dropdown.dart: Uses shadcn.Popover and shadcn.OutlinedContainer.
• querya_modal_dialog.dart: Uses shadcn.Dialog.
• querya_search_field.dart: Uses shadcn.TextField.
• querya_tab_strip.dart: Uses shadcn.Tab and shadcn container wrappers.
• querya_spinner.dart: Uses shadcn.CircularProgressIndicator.

Moving these to own implementations built on Flutter primitives (OverlayPortal / RawKeyboardListener / CustomPainter) removes external library constraints, unifies control scale tokens, and eliminates frame hitches from complex shadcn widget trees.

Subtasks

• Migrate QueryaDropdown from shadcn.Popover to an OverlayPortal-based native popup trigger.
• Migrate QueryaModalDialog and showAppDialog to pure showGeneralDialog with Querya theme tokens.
• Migrate QueryaSearchField to a pure material.TextField / EditableText wrapper with Querya search icons.
• Migrate QueryaSpinner to a lightweight CustomPainter with theme accent.
• Add guard test test/guards/shared_does_not_import_shadcn_test.dart to prevent regressions.

Acceptance Criteria

• No file in lib/shared/widgets/ imports package:shadcn_flutter.
• All existing dialog, dropdown, search, and navigation tests pass.
• Visual regression tests in the UI kit gallery match current design tokens.