feat: unify modal UX with frosted panels, icons and filled focus

[nextestudios]

Summary

One modal system for every modal surface (menus, confirmations, warnings, errors, password/on-screen keyboard, Operations center and details, results, folder-picker menu, Properties, About, controller test/setup, image/text previews):

• Panel: dimmed page, frosted panel (WinUI acrylic, tint #0C1B2A) with ~22 px corners, thin light edge and ThemeShadow; header with a tone badge icon, title (UIA ControlFS.ModalTitle kept) and context line; divider; scrollable body; footer with the current status message and the controller prompts inside the panel (same ControllerPromptProvider/glyphs, only working actions; the window footer hints fade out without reflow).
• Rows: full-width option rows with a leading icon + label (+ detail line); focused = filled cyan with dark SemiBold text, scaled 1.025 (non-color cues: fill shape, weight, size). Destructive: red + trailing warning symbol, red fill when focused. Disabled: dimmed, focused shows "Indisponível: reason". Section headings in menus (App menu: Nesta pasta / Exibição / Operações / Controles / ControlFS; item menus: Abrir / Organizar / Favoritos / Esta pasta / Seleção / Informações). Order of items unchanged.
• Icons in one place: ActionIcon enum + ActionIcons.Glyph (Segoe Fluent/MDL2) + ActionIcons.IsDestructive in Core; MenuItem.Icon/Section, DialogOption.Icon, Modal.Icon/Subtitle, DialogModal.Progress set by AppController (no WinUI in Core/Application). Result/error dialogs get success/warning/error tone.
• Safety: AppController.SafeInitialFocus guarantees no menu/dialog opens focused on a destructive option. Narrator appends "ação perigosa".
• Accessibility fallbacks: transparency effects off or high contrast → solid panel + darker scrim (Theme.SolidSurfaces, from UISettings.AdvancedEffectsEnabled / AccessibilitySettings.HighContrast, re-read on AdvancedEffectsEnabledChanged/ColorValuesChanged); Windows animations off → no transition. Only animation: 120 ms opacity on a new modal; input never waits.
• Keyboard keys and previews restyled in the same language; previews measure header/footer so text paging and image fit stay exact.

Tests

• New ModalSystemJourneyTests (4): icon for every menu option/dialog button across main menus and dialogs + every icon has a glyph; destructive flagged and never initial focus (menus and dialogs); input under a modal never reaches the screen (buttons, list click, tab click); nested modals (keyboard over Compactar dialog) close one at a time and restore focus.
• build/Test-UiAutomation.ps1: danger option now reads Sair (the ⚠ moved from text to an icon); all other UIA checks unchanged. Smoke (UIA, launches, installer, render-screens) green on this branch.
• --render-screens: new captures m1…m9 (menu, destructive focus, delete confirmation frosted + solid, extract summary, password, password error, success result, error, operations, operation details, picker menu, About) at 1280×720, 1280×800, 1920×1080, 3840×2160 at 100% and 200%, plus icons/action-icons.png. All report "cabe" (fit). Reviewed visually.

Manual (not hardware validated)

Added "Modais (#172)" to docs/TESTING.md: TV distance, real Xbox/PlayStation/Nintendo/generic controllers, transparency off, high contrast, animations off, shadow (RenderTargetBitmap doesn't draw it), mouse, Narrator.

Docs: CHANGELOG pair, GUIDE pair ("Menus and dialogs"), docs/ui-redesign.md (phase M, modal tokens, matrix row).

Closes #172

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