Isolate repository validation from generated worktrees

[ProGraMajster]

Summary

Repository-level validation now distinguishes tracked source files from generated artifacts and nested worktrees, eliminating false positives without hiding real source-tree inconsistencies.

Root cause

ReleaseVersionConsistencyTests previously scanned the filesystem recursively and could discover projects inside artifacts/, including complete nested worktrees with historical package versions.

Solution

• prefer tracked-file enumeration through local git ls-files when Git metadata is available
• provide a bounded, safe filesystem fallback for source archives and unavailable Git metadata
• exclude generated directories by complete path segment rather than substring
• normalize the repository root and reject unsafe or escaping paths
• prune nested worktrees represented by either a .git directory or worktree file
• avoid following reparse points, symlinks, and junctions
• return deterministic, ordinally sorted repository-relative results and diagnostics

Regression coverage

Coverage includes:

• generated artifacts content and complete nested worktrees
• bin and obj
• nested .git directories and worktree files
• similarly named source directories such as ArtifactsDocumentation, BinaryTools, and ObjectModel
• Windows and Unix path separators and case handling
• repository-root resolution and no-Git fallback
• unsafe path traversal and reparse points
• confirmation that a real source-tree version inconsistency is still detected

Validation

• dotnet restore .\ModernFormsNext.slnx: passed
• full Debug build: passed, 0 warnings / 0 errors
• full Release build: passed, 0 warnings / 0 errors
• all automated tests: 1140/1140 passed
• RepositoryFileEnumeratorTests: 28/28 passed
• ReleaseVersionConsistencyTests: 5/5 passed with three existing nested worktrees under artifacts/
• release documentation script tests: 32/32 assertions passed
• VSIX Debug and Release validation: passed, 0 warnings / 0 errors
• release packages: 8 NuGet and 7 symbol packages validated
• git diff --check: passed

Closes #83