Step NC03: Desktop App Shell And Theme

[deku2026]

Summary

• Implements Step NC03: Desktop App Shell And Theme
• Keeps scope limited to the active step
• Updates traceability and acceptance evidence required by the step

Verification

• $env:MSBUILDDISABLENODEREUSE='1'; dotnet restore ArcChat.slnx -m:1: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet build ArcChat.slnx -m:1 --no-restore: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet test ArcChat.slnx -m:1 --no-build --blame-hang-timeout 120s: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet test apps\desktop\ArcChat.Desktop.UiTests\ArcChat.Desktop.UiTests.csproj -m:1 --no-build --blame-hang-timeout 120s: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet test desktop-shared\ArcChat.UI.Theme.Tests\ArcChat.UI.Theme.Tests.csproj -m:1 --no-build --blame-hang-timeout 120s: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet test desktop-shared\ArcChat.UI.Controls.Tests\ArcChat.UI.Controls.Tests.csproj -m:1 --no-build --blame-hang-timeout 120s: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet format ArcChat.slnx --verify-no-changes --no-restore: passed
• $env:MSBUILDDISABLENODEREUSE='1'; pwsh -NoLogo -NoProfile -ExecutionPolicy Bypass -File scripts\verify-notice.ps1: passed
• $env:MSBUILDDISABLENODEREUSE='1'; dotnet run --project apps\desktop\ArcChat.Desktop --no-build: boot smoke stayed alive for 5 seconds, then stopped

Traceability

• Rows updated: NC-UI-001, NC-UI-002, NC-UI-003, NC-UI-004, NC-UI-005, NC-UI-006, NC-UI-007, NC-FEAT-024, NC-FEAT-025
• Matrices updated: docs/coverage/nc03-desktop-shell-theme.md, docs/coverage/settings-schema.md, docs/coverage/visual-baseline/README.md
• Final-gate impact: NC03 shell/theme accessibility, visual baseline, locale/theme runtime switching, and settings evidence are now covered by tests and reproducible artifacts

Out Of Scope

• Conversation feature (NC04)
• Providers (NC05/NC06)
• Masks/plugins beyond shell placeholders (NC07)

Open Questions

• None