🗃️ Add database schema, models & seeders (Story 1.2)

Migrations (translations, projects, skills, skill_project), Eloquent models
with belongsToMany relations, scopes, and test seeders (74 translations FR/EN,
10 skills, 3 projects, 12 skill-project links).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

api/app/Models/Translation.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Builder;
+
+class Translation extends Model
+{
+    protected $fillable = ['lang', 'key_name', 'value'];
+
+    public function scopeForLang(Builder $query, string $lang): Builder
+    {
+        return $query->where('lang', $lang);
+    }
+
+    public static function getTranslation(string $key, string $lang, string $fallback = 'fr'): ?string
+    {
+        $translation = static::where('key_name', $key)->where('lang', $lang)->first();
+
+        if (!$translation && $lang !== $fallback) {
+            $translation = static::where('key_name', $key)->where('lang', $fallback)->first();
+        }
+
+        return $translation?->value;
+    }
+}