feat: L'Ami Fiduciaire V1.0.0 — full codebase with Story 0.1 complete

Initial commit of the L'Ami Fiduciaire SaaS platform built on Laravel 12,
Vue 3, Inertia.js 2, and Tailwind CSS 4.

Story 0.1 (rename folders to declarations in database) is implemented and
code-reviewed: migration, rollback, and 6 Pest tests all passing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Models/FolderInvitation.php

@@ -0,0 +1,72 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Support\Str;
+
+class FolderInvitation extends Model
+{
+    /**
+     * The attributes that are mass assignable.
+     *
+     * @var list<string>
+     */
+    protected $fillable = [
+        'folder_id',
+        'token',
+        'email',
+        'expires_at',
+        'used_at',
+    ];
+
+    /**
+     * Get the attributes that should be cast.
+     *
+     * @return array<string, string>
+     */
+    protected function casts(): array
+    {
+        return [
+            'expires_at' => 'datetime',
+            'used_at' => 'datetime',
+        ];
+    }
+
+    /**
+     * Boot the model.
+     */
+    protected static function boot(): void
+    {
+        parent::boot();
+
+        static::creating(function (FolderInvitation $invitation) {
+            if (empty($invitation->token)) {
+                $invitation->token = Str::uuid()->toString();
+            }
+        });
+    }
+
+    /**
+     * Get the folder that owns the invitation.
+     *
+     * @return BelongsTo<Folder, $this>
+     */
+    public function folder(): BelongsTo
+    {
+        return $this->belongsTo(Folder::class);
+    }
+
+    /**
+     * Check if the invitation is valid (not expired, not used).
+     */
+    public function isValid(): bool
+    {
+        if ($this->used_at !== null) {
+            return false;
+        }
+
+        return $this->expires_at->isFuture();
+    }
+}