chore(repo): restructure src/tests/.assets layout + drop Matt-era IDE files

[ChrisonSimtian]

Repo cleanup and reshape. No behavior change in shipping code; build, slnx, and test references are updated to track.

Structural changes

From	To
source/Nuke.*/ (production)	src/Nuke.*/
source/Nuke.*.Tests/	tests/Nuke.*.Tests/
images/	.assets/images/
icon.png (root)	.assets/icon.png
source/Directory.Build.props	Directory.Build.props (root)
source/AssemblyInfo.cs	AssemblyInfo.cs (root)

Directory.Build.props was hoisted to root so both src/ and tests/ inherit via MSBuild's directory walk. Paths inside it now use $(MSBuildThisFileDirectory) so they're depth-independent. Added a ManagePackageVersionsCentrally != false condition on the SourceLink/NB.GV refs so they don't leak into _build.csproj.

Removed (Matt-era / no longer applicable)

File	Why
.editorconfig	2017-vintage copy from the Roslyn repo. Relying on dotnet format defaults going forward.
nuke-common.sln.DotSettings	ReSharper config — we don't use Rider/R#.
source/CodeStyle.DotSettings	ReSharper code style.
source/Inspections.DotSettings	ReSharper inspection severities.
.run/ (6 files)	JetBrains Rider run configurations.
GitVersion.yml	Referenced master/develop branches; we're on Nerdbank.GitVersioning.
external/	Orphan submodule placeholder pointing at Matt's NUKE ecosystem repos (website/promo/resharper). Not used by build. .gitignore already said ignore it.
Dockerfile	Referenced dotnet/sdk:8.0 (we're on 10), not invoked by any CI workflow.

Stripped

• TFS leftover in nuget.config (root) and src/Nuke.GlobalTool/templates/nuget.config:

  <solution>
    <add key="disableSourceControlIntegration" value="true" />
  </solution>

  Property only matters under TFVC; useless on git.

SLNX cleanup

• Removed bogus Type="Classic C#" attribute from every <Project> entry. These are SDK-style projects; the attribute was a half-baked sln→slnx migration artifact (some projects had it, some didn't).

Docs

• New: docs/architecture.md — canonical layout doc, linked from CLAUDE.md. Describes top-level structure, project groupings under src/, build conventions, CI layout.
• Updated CLAUDE.md — codifies the src//tests//docs//.assets/ convention so future AI sessions track the new structure. Also drops the ReSharper/.editorconfig mentions.
• Updated CONTRIBUTING.md — tool wrapper path source/ → src/.
• Updated tests/Nuke.Common.Tests/GitHubTasksTest.cs — uses src/ in fixture paths.
• Updated .github/workflows/ubuntu-latest.yml — paths-ignore: images/** → .assets/**.
• Updated build/Build.CI.GitHubActions.cs — same paths-ignore change in the generator source so future regenerations stay consistent.
• Updated CHANGELOG.md — vNext entry.

Verification

• dotnet build nuke-common.slnx -c Debug — 0 warnings, 0 errors.
• All test projects compile (build pulls them in).
• _build.csproj builds (was the trickiest after hoisting Directory.Build.props).
• Git tracked all moves as renames (no add/delete pairs).

Out of scope (later issues)

• Tool JSON $schema URLs still reference nuke-build/nuke/master/source/... — these are upstream schema URLs; updating to our fork is part of [P2] Audit and update string references to nuke.build, nuke-build/nuke, etc. #30 (audit string references).
• *.Generated.cs files still have stale // Generated from .../source/... comments — they regenerate from git origin on next ./build.ps1 GenerateTools.

Test plan

• CI passes on ubuntu-latest.
• Visual sanity check on the GitHub README rendering with new image paths.
• After merge: confirm windows-latest and macos-latest post-merge runs pass with the new layout.

🤖 Generated with Claude Code