🗃️ 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/Skill.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
+
+class Skill extends Model
+{
+    protected $fillable = [
+        'slug',
+        'name_key',
+        'description_key',
+        'icon',
+        'category',
+        'max_level',
+        'display_order',
+    ];
+
+    public function projects(): BelongsToMany
+    {
+        return $this->belongsToMany(Project::class, 'skill_project')
+            ->withPivot(['level_before', 'level_after', 'level_description_key'])
+            ->withTimestamps();
+    }
+
+    public function scopeByCategory(Builder $query, string $category): Builder
+    {
+        return $query->where('category', $category);
+    }
+
+    public function scopeOrdered(Builder $query): Builder
+    {
+        return $query->orderBy('display_order');
+    }
+}