Operad v9.0.0

• Added element material and shader-effect support for UI surfaces, including
  shader-backed canvas, frame, and button previews, paint outsets, clip and hit
  shape controls, geometry-effect declarations, and renderer-safe fallback
  reporting for invalid WGSL.
• Added the Shader Lab showcase for editable WGSL programs, program presets,
  material contract controls, canvas/frame/button targets, and live validation
  without crashing the host when shader compilation fails.
• Hardened popup, dropdown, menu, tooltip, modal, and portal stacking so
  anchored surfaces are layered relative to their owning window and stay above
  later siblings without escaping unrelated floating windows.
• Reworked scroll containers and scrollbars with automatic visibility,
  reserved scrollbar gutters, hover/active visual states, draggable thumbs,
  ctrl/shift horizontal scrolling, end-position tests, and range epsilon fixes.
• Improved text editing and selection ownership, including single active text
  selection, tighter caret and selection geometry, focus blur behavior,
  multiline newline handling, and scrollable code/text editor regions.
• Expanded media and image resources with user-supplied image handles, decoded
  PNG/JPEG/BMP assets, clearer missing-image rendering, icon image variants,
  and showcase coverage for image-backed checkbox marks and media grids.
• Added indeterminate checkbox state, richer radio/toggle customization,
  editable numeric inputs with unit-specific ranges, date range picking,
  progress logs, theme switching, panel resizing, timeline scrolling, editable
  trees, and easing demos.
• Refined showcase layout and organization behavior so windows start closer to
  content size, can be packed/minimized when organized, and keep regressions in
  external tests instead of examples/showcase.rs.
• Cleaned up all-target Cargo warnings and extended visual/layout tests for the
  v9 widget surfaces.