workspace: fix test registry pollution, rename to managed-projects.json, slug-based entries

[Allann]

Problem

Running tests was polluting the real user registry (%LOCALAPPDATA%\AiDevStudio\registry.json) with stale "Demo Project" entries from temp directories. Every call to WorkspaceService.CreateProject → RegisterPath wrote to the production registry file, so repeated test runs accumulated junk entries visible in the WinUI app.

Changes

Core: registry isolation

• WorkspaceService — added optional string? registryFilePath parameter and EffectiveRegistryFile property. When non-null, all registry reads/writes use this path instead of the global one. Tests pass a temp path; production DI path is unaffected.
• CoreServiceExtensions.AddAiDevCore — removed ActiveWorkspaceHolder/WorkspacePaths from the shared DI registration (hosts register those themselves); uses an explicit factory for WorkspaceService to avoid DI constructor ambiguity in .NET 10.

Core: registry refactor

• FilePathConstants — renamed constant to ManagedProjectsFileName = "managed-projects.json"
• GlobalPaths — ManagedProjectsFile property replaces RegistryFile; filename is now managed-projects.json
• WorkspaceRegistryEntry — added Slug property so each entry stores { path, slug }
• WorkspaceService — RegisterPath → RegisterEntry(path, slug); stores both fields

Tests: full isolation

All test classes now use a temp registry path — no test will ever write to the real user registry:

File	Fix
WorkspaceServiceTests	IDisposable, temp _registryPath, passed to constructor
ConsistencyCheckServiceTests	same pattern
ProductionReadinessIntegrationTests	temp registry; assertion updated from GlobalPaths.RegistryFile → temp path
ConsistencyUiAndDetectionIntegrationTests	temp registry
ProjectSettingsViewModelTests	temp registry, fixed WorkspacePaths root alignment, AgentExecutorName typed properties
DecisionsViewModelTests	IAgentInboxService arg, .Value.ShouldBe() for DecisionId, CS4014 fix

WinUI: csproj hygiene

• Scoped PublishReadyToRun/PublishTrimmed to publish-only targets to avoid spurious build warnings
• Updated App.xaml.cs to reference GlobalPaths.ManagedProjectsFile

Result

• ✅ 0 build warnings/errors
• ✅ All unit, integration, and WinUI tests pass without touching production data