refactor: restructure project layout and rewrite diff engine

- Move library from BlazorTextDiff/ to src/BlazorTextDiff/
- Update solution file with src/tests directory structure
- Upgrade packages: AspNetCore 9.0.8 -> 9.0.13, DiffPlex 1.8.0 -> 1.9.0
- Remove JS interop (BlazorTextDiff.js) - pure C#/Blazor now
- Remove SCSS pipeline (compilerconfig.json, BlazorDiff.scss)
- Remove stale docs/ directory
- Rewrite TextDiff.razor: use CharacterChunker for per-character diffs,
  add IgnoreWhiteSpace post-processing, Class/AdditionalAttributes params
- Rewrite TextDiffLine.razor: word+character two-tier highlighting with
  word grouping logic for partial and fully changed words
- Fix DiffStats to count deletions from OldText pane (was always 0)
- Add interactive collapse/expand toggle

Author: lzinga

BlazorTextDiff.sln

@@ -3,28 +3,71 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.3.32929.385
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BlazorTextDiff", "BlazorTextDiff\BlazorTextDiff.csproj", "{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}"
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BlazorTextDiff.Web", "BlazorTextDiff.Web\BlazorTextDiff.Web.csproj", "{3D074FDC-FD1B-4E1E-9A9E-030727444A66}"
+Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "tests", "tests", "{B2C3D4E5-F6A7-8901-BCDE-F12345678901}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BlazorTextDiff", "src\BlazorTextDiff\BlazorTextDiff.csproj", "{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BlazorTextDiff.Web", "src\BlazorTextDiff.Web\BlazorTextDiff.Web.csproj", "{3D074FDC-FD1B-4E1E-9A9E-030727444A66}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BlazorTextDiff.Tests", "tests\BlazorTextDiff.Tests\BlazorTextDiff.Tests.csproj", "{D9CCECCD-F332-465C-8584-065F477AD15D}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
 		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
 	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Debug|x64.Build.0 = Debug|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Debug|x86.Build.0 = Debug|Any CPU
 		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Release|Any CPU.Build.0 = Release|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Release|x64.ActiveCfg = Release|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Release|x64.Build.0 = Release|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Release|x86.ActiveCfg = Release|Any CPU
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8}.Release|x86.Build.0 = Release|Any CPU
 		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Debug|x64.Build.0 = Debug|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Debug|x86.Build.0 = Debug|Any CPU
 		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Release|Any CPU.Build.0 = Release|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Release|x64.ActiveCfg = Release|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Release|x64.Build.0 = Release|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Release|x86.ActiveCfg = Release|Any CPU
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66}.Release|x86.Build.0 = Release|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Debug|x64.Build.0 = Debug|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Debug|x86.Build.0 = Debug|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Release|x64.ActiveCfg = Release|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Release|x64.Build.0 = Release|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Release|x86.ActiveCfg = Release|Any CPU
+		{D9CCECCD-F332-465C-8584-065F477AD15D}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection
+	GlobalSection(NestedProjects) = preSolution
+		{8268065C-5552-47C2-B8DE-38EFF8A0F0E8} = {A1B2C3D4-E5F6-7890-ABCD-EF1234567890}
+		{3D074FDC-FD1B-4E1E-9A9E-030727444A66} = {A1B2C3D4-E5F6-7890-ABCD-EF1234567890}
+		{D9CCECCD-F332-465C-8584-065F477AD15D} = {B2C3D4E5-F6A7-8901-BCDE-F12345678901}
+	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {7B508BCF-52CC-4CB1-9F82-F85A4CDC4A16}
 	EndGlobalSection