refactor: Cleanup git state - commit all staged changes

Major refactoring cleanup:
- Add new controller architecture (class-controller-*.php)
- Add new settings-v2 UI (views/settings-v2/)
- Add new CSS architecture (agentic-sidebar.css, tokens)
- Add esbuild build pipeline (scripts/build.js, package.json)
- Add composer dependencies (vendor/)
- Add frontend src directory (assets/js/src/index.jsx)
- Add documentation files
- Remove old/obsolete files (class-settings.php, old CSS)

This commits all pending changes from previous refactoring efforts.

vendor/league/flysystem/deprecations.md

@@ -0,0 +1,19 @@
+# Deprecations
+
+This document lists all the planned deprecations.
+
+## Handlers will be removed in 2.0
+
+The `Handler` type and associated calls will be removed in version 2.0.
+
+### Upgrade path
+
+You should create your own implementation for handling OOP usage,
+but it's recommended to move away from using an OOP-style wrapper entirely.
+
+The reason for this is that it's too easy for implementation details (for
+your application this is Flysystem) to leak into the application. The most
+important part for Flysystem is that it improves portability and creates a
+solid boundary between your application core and the infrastructure you use.
+The OOP-style handling breaks this principle, therefore I want to stop
+promoting it.