Add Expand() to AbsolutePath and RelativePath

Add FileSystemPath.Resolve for cross-platform path translation

Static class with platform detection in static ctor (no branching per call).
On Linux/WSL: converts Windows drive paths (D:\source) to /mnt/d/source.
On Windows: converts /mnt/d/source to D:\source.
Non-drive paths get separator normalization only.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Add Length property to AbsolutePath and RelativePath

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Add FileSystem.Blazor package with FileExplorer component

Add Sha1.Compute and Sha256.Compute factory methods

Add Sha1, Sha256 value types and IFileSystem abstraction

Add path + extension operators

- RelativePath + FileExtension = RelativePath
- AbsolutePath + FileExtension = AbsolutePath

Example: "document" + FileExtension.Txt => "document.txt"

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Breaking: Strongly-typed API with FileExtension value type

BREAKING CHANGES:
- Remove Value property (use implicit string conversion)
- Remove Exists, IsFile, IsDirectory (no filesystem access)
- Remove CurrentDirectory (no filesystem access)
- FileName now returns RelativePath instead of string
- Root now returns AbsolutePath? instead of string
- Extension now returns FileExtension instead of string

NEW:
- FileExtension value type with WithDot/WithoutDot properties
- Common extensions: Txt, Json, Cs, Md, etc.
- IsOneOf() for extension matching
- FileNameWithoutExtension property
- ChangeExtension() method

99 tests passing.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Add NuGet package metadata with README

- Package description, tags, license (MIT)
- Include README.md in NuGet package
- Repository and project URLs

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Fix line endings in release.sh