Add identity_type and guardian relationship to members

- Add identity_type field (patient/parent) to distinguish 病友/家長
- Add guardian_member_id for parent-child relationships
- Add guardian() and dependents() relationships
- Add isPatient(), isParent() helper methods
- Add identity_type_label accessor

Data updated:
- 47 members set as patient, 4 as parent
- 25 members with approved disability, 26 without
- 張序 linked to guardian 張誠駿
- Payment amounts corrected based on 2024 accounting records

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

app/Models/Member.php

@@ -30,6 +30,10 @@ class Member extends Model
     const DISABILITY_STATUS_APPROVED = 'approved';
     const DISABILITY_STATUS_REJECTED = 'rejected';
 
+    // Identity type constants (病友/家長)
+    const IDENTITY_PATIENT = 'patient';   // 病友
+    const IDENTITY_PARENT = 'parent';     // 家長/父母
+
     protected $fillable = [
         'user_id',
         'full_name',
@@ -47,6 +51,8 @@ class Member extends Model
         'membership_expires_at',
         'membership_status',
         'membership_type',
+        'identity_type',
+        'guardian_member_id',
         'disability_certificate_path',
         'disability_certificate_status',
         'disability_verified_by',
@@ -72,6 +78,50 @@ class Member extends Model
         return $this->hasMany(MembershipPayment::class);
     }
 
+    /**
+     * 監護人（父母）
+     */
+    public function guardian()
+    {
+        return $this->belongsTo(Member::class, 'guardian_member_id');
+    }
+
+    /**
+     * 被監護人（子女）
+     */
+    public function dependents()
+    {
+        return $this->hasMany(Member::class, 'guardian_member_id');
+    }
+
+    /**
+     * 是否為病友
+     */
+    public function isPatient(): bool
+    {
+        return $this->identity_type === self::IDENTITY_PATIENT;
+    }
+
+    /**
+     * 是否為家長/父母
+     */
+    public function isParent(): bool
+    {
+        return $this->identity_type === self::IDENTITY_PARENT;
+    }
+
+    /**
+     * 取得身份類型標籤
+     */
+    public function getIdentityTypeLabelAttribute(): string
+    {
+        return match ($this->identity_type) {
+            self::IDENTITY_PATIENT => '病友',
+            self::IDENTITY_PARENT => '家長/父母',
+            default => '未設定',
+        };
+    }
+
     /**
      * 關聯的收入記錄
      */