Implement ID-based routing and folder auto-generation from titles

Major features:
- Switch from slug-based to ID-based routing (/documents/123)
- Enable title editing with automatic slug/path regeneration
- Auto-generate folder structure from title slashes (e.g., Laravel/Livewire/Components)
- Persist sidebar folder open/close state using localStorage
- Remove slug unique constraint (ID routing makes it unnecessary)
- Implement recursive tree view with multi-level folder support

Architecture changes:
- DocumentService: Add generatePathAndSlug() for title-based path generation
- Routes: Change from {document:slug} to {document} for ID binding
- SidebarTree: Extract recursive rendering to partials/tree-item.blade.php
- Database: Remove unique constraint from documents.slug column

UI improvements:
- Display only last path component in sidebar (Components vs Laravel/Livewire/Components)
- Folder state persists across page navigation via localStorage
- Title field accepts slashes for folder organization

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/app/Helpers/SlugHelper.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Helpers;
+
+use Cocur\Slugify\Slugify;
+use Illuminate\Support\Str;
+
+class SlugHelper
+{
+    /**
+     * Generate a slug from a title, supporting Japanese and other non-ASCII characters
+     *
+     * @param string $title
+     * @param string|null $fallback Optional fallback if slug is empty
+     * @return string
+     */
+    public static function generate(string $title, ?string $fallback = null): string
+    {
+        $slugify = new Slugify(['lowercase' => true]);
+
+        // Try to generate slug with cocur/slugify
+        $slug = $slugify->slugify($title);
+
+        // If slug is empty (happens with pure Japanese/Chinese characters),
+        // use fallback or generate a unique identifier
+        if (empty($slug)) {
+            if ($fallback) {
+                $slug = $fallback;
+            } else {
+                // Use timestamp + random string for unique slug
+                $slug = date('YmdHis') . '-' . Str::random(8);
+            }
+        }
+
+        return $slug;
+    }
+}