chore: reorganize snippets into subdirectories

- move root gitignores into gitignores/ subdirectory
- add gitignores for dart, dotnet, go, gradle, java, jetbrains, maven, nextjs, node, sublimetext, vscode, windows, xcode
- add root .gitignore excluding .claude/settings.local.json
- add empty README.md and licences/ placeholders (Apache, MIT, Mozilla)

gitignores/VisualStudioCode.gitignore

@@ -0,0 +1,11 @@
+### Visual Studio Code
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/*.code-snippets
+!*.code-workspace
+
+# Built Visual Studio Code Extensions
+*.vsix