feat(阶段三): 添加知识库模型和迁移

- 创建 knowledge_bases 表迁移
- 创建 KnowledgeBase 模型
- 创建 KnowledgeBaseFactory 工厂类
- 支持与终端的多对多关联关系

app/Models/KnowledgeBase.php

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+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\SoftDeletes;
+
+class KnowledgeBase extends Model
+{
+    use HasFactory, SoftDeletes;
+
+    /**
+     * 可批量赋值的属性
+     *
+     * @var array<string>
+     */
+    protected $fillable = [
+        'name',
+        'description',
+        'status',
+    ];
+
+    /**
+     * 获取关联的终端
+     *
+     * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany
+     */
+    public function terminals()
+    {
+        return $this->belongsToMany(Terminal::class, 'terminal_knowledge_bases')
+                    ->withPivot('priority')
+                    ->withTimestamps()
+                    ->orderBy('priority');
+    }
+}

database/factories/KnowledgeBaseFactory.php

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+<?php
+
+namespace Database\Factories;
+
+use App\Models\KnowledgeBase;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends \Illuminate\Database\Eloquent\Factories\Factory<\App\Models\KnowledgeBase>
+ */
+class KnowledgeBaseFactory extends Factory
+{
+    protected $model = KnowledgeBase::class;
+
+    /**
+     * Define the model's default state.
+     *
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        return [
+            'name' => $this->faker->words(3, true),
+            'description' => $this->faker->sentence(),
+            'status' => $this->faker->randomElement(['active', 'inactive']),
+        ];
+    }
+
+    /**
+     * 指定知识库为激活状态
+     */
+    public function active(): static
+    {
+        return $this->state(fn (array $attributes) => [
+            'status' => 'active',
+        ]);
+    }
+
+    /**
+     * 指定知识库为非激活状态
+     */
+    public function inactive(): static
+    {
+        return $this->state(fn (array $attributes) => [
+            'status' => 'inactive',
+        ]);
+    }
+}

database/migrations/2026_03_09_022236_create_knowledge_bases_table.php

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+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('knowledge_bases', function (Blueprint $table) {
+            $table->id();
+            $table->string('name')->comment('知识库名称');
+            $table->text('description')->nullable()->comment('知识库描述');
+            $table->string('status')->default('active')->comment('状态');
+            $table->timestamps();
+            $table->softDeletes();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('knowledge_bases');
+    }
+};