Clean up .gitignore to only cover project-specific artifacts

Remove the broad hidden file exclusion and its `.git*` whitelist in
favor of a global `~/.gitignore`. Editor and OS artifacts such as
`.DS_Store`, `.idea/`, or `.vscode/` are environment-specific and not
the project's responsibility to exclude.

Each developer should maintain a global ignore file for such artifacts:

    git config --global core.excludesFile ~/.gitignore

Keep only Composer installation artifacts with a comment clarifying
why `composer.lock` is excluded for library projects.

Author: lippserd

.gitignore

@@ -1,10 +1,5 @@
-# Exclude all hidden files
-.*
-
-# Except those related to Git and GitHub
-!.git*
-!.github*
-
-# Exclude files from composer install
-vendor/
+# Ignore Composer installation artifacts; composer.lock is intentionally
+# excluded as this is a library - applications depending on this package
+# manage their own lock file.
+/vendor/
 composer.lock