Introduce unified material/color spec and tests, and refactor appearance plumbing to use MaterialColorSnapshot as the single source of truth. Add .trae material-color-service spec/checklist/tasks and integration/unit tests for plugin mapping and appearance VM behavior. AppearanceChangedEvent extended with new appearance change flags and HasChanged logic. ComponentEditorMaterialThemeAdapter rewritten to accept MaterialColorSnapshot and derive palette from snapshot data. Simplify AppearanceSettingsPageViewModel and related view code: remove legacy preview/custom-seed UI logic, preserve material/color fields when updating theme or corner radius, and update save calls to use with-expressions. Update ComponentEditorWindow to use adapter-provided OnPrimary brush and minor docs updates.
Rebuild the settings window as a Fluent shell: adds a custom 48-DIP titlebar with Back, pane toggle, icon/title, search box, restart/more menu, and caption-button spacer; moves compact pane toggle into the titlebar and preserves FANavigationView as the primary navigation surface. Introduces a SettingsSearchService (with UI AutoComplete integration, search indexing, navigation-by-result, and search result highlighting) plus focused tests for search filtering and theme material normalization. Adds navigation history/back stack, updates SettingsViewModels for new bindings and localization keys, and updates General/Apearance pages to expose new strings and options. Implements an "auto" system material mode: default in AppSettingsSnapshot, new MaterialAuto constants and normalization/resolution logic in ThemeAppearanceValues, WindowMaterialService and MaterialSurfaceService adjustments to prefer Mica on Win11 and Acrylic on Win10 using TransparencyLevelHint. GlassEffectService and AppearanceThemeService updated to use effective material mode and to track live theme state changes. Adds localization entries (en-US, zh-CN), spec/tasks docs, and other UI/style tweaks to support the redesign.
