feat(project): generate sky and environment lighting defaults

[JeanPhilippeKernel]

New projects now explicitly include the engine's sky authoring defaults and environment-lighting policy in projectConfig.json: atmosphere mode, intensity 1, white RGBA tint, zero yaw, quality standard, and a 384 MiB integer budget. Environment maps remain optional asset UUIDs.

Additional rendering properties survive configuration serialization. Existing project files are not migrated, and renaming preserves their rendering settings and legacy sky data. The project configuration guide documents quality tiers, memory units, compatibility, and scene ownership.

Closes #74
Closes #75
Closes #76

Validation:

• dotnet build Panzerfaust.csproj --no-restore succeeded.
• Serialization checks passed for defaults, optional UUIDs, all quality tiers, custom rendering properties, and missing settings.
• Integration checks exercised actual project creation, directory scaffolding, metadata persistence, rename preservation, and legacy configuration compatibility; temporary test data was removed.
• The rebuilt desktop app launched and remained running.
• git diff --check passed.

NuGet's vulnerability metadata check remained unavailable. Visual UI behavior and opening a generated project in the engine editor have not been verified. Verification harnesses ran from temporary directories and are not included in this PR.