feat:實作 Coach Portal — 教練後台課程管理

後端：
- Migration：diving_offers 新增 provider_id（nullable FK）
- Migration：users.role ENUM 加入 provider 值
- Migration：diving_offers.spot 改為 nullable
- AuthController：registerProvider business_name 改為選填
- AuthController：updateProviderProfile 補上 certifications / dive_sites / services / facilities / website / social_media
- ProviderOfferController：教練課程 CRUD（index/show/store/update/destroy），實作 provider_id 所有權不變式（404 → 403 兩步驟）

前端（frontend/）：
- coachAuth store、coachAxios（獨立於 member auth）
- /coach/* 路由群組 + beforeEach guard
- CoachNavBar、CoachLayout（教練頁隱藏會員 NavBar）
- LoginView、RegisterView、DashboardView（表格 + 刪除確認）
- OfferFormView（新增/編輯共用）、ProfileView

OpenSpec：
- openspec/config.yaml 補入專案 context 與 rules
- 新增 specs：coach-offers-api / coach-portal-ui / provider-auth
- 更新 spec：diving-offers-api 加入 provider_id
- 歸檔：openspec/changes/archive/2026-05-10-coach-portal

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

app/Http/Controllers/API/AuthController.php

@@ -474,7 +474,7 @@ class AuthController extends Controller
             'email' => 'required|string|email|max:255|unique:users',
             'password' => 'required|string|min:6|confirmed',
             'phone' => 'nullable|string|max:20',
-            'business_name' => 'required|string|max:255',
+            'business_name' => 'nullable|string|max:255',
             'description' => 'nullable|string',
             'contact_person' => 'nullable|string|max:100',
             'contact_phone' => 'nullable|string|max:20',
@@ -655,6 +655,12 @@ class AuthController extends Controller
             'contact_email' => 'nullable|string|email|max:255',
             'address' => 'nullable|string|max:255',
             'business_hours' => 'nullable|string|max:100',
+            'certifications' => 'nullable|string',
+            'dive_sites' => 'nullable|string',
+            'services' => 'nullable|string',
+            'facilities' => 'nullable|string',
+            'website' => 'nullable|string|max:255',
+            'social_media' => 'nullable|string|max:255',
         ]);
 
         if ($validator->fails()) {
@@ -701,7 +707,25 @@ class AuthController extends Controller
         if ($request->has('business_hours')) {
             $providerProfile->business_hours = $request->business_hours;
         }
-        
+        if ($request->has('certifications')) {
+            $providerProfile->certifications = $request->certifications;
+        }
+        if ($request->has('dive_sites')) {
+            $providerProfile->dive_sites = $request->dive_sites;
+        }
+        if ($request->has('services')) {
+            $providerProfile->services = $request->services;
+        }
+        if ($request->has('facilities')) {
+            $providerProfile->facilities = $request->facilities;
+        }
+        if ($request->has('website')) {
+            $providerProfile->website = $request->website;
+        }
+        if ($request->has('social_media')) {
+            $providerProfile->social_media = $request->social_media;
+        }
+
         $providerProfile->save();
 
         // 加載服務提供者資料

app/Http/Controllers/API/ProviderOfferController.php

@@ -0,0 +1,111 @@
+<?php
+
+namespace App\Http\Controllers\API;
+
+use App\Http\Controllers\Controller;
+use App\Models\DivingOffer;
+use Illuminate\Http\Request;
+
+class ProviderOfferController extends Controller
+{
+    public function index()
+    {
+        $offers = DivingOffer::where('provider_id', auth()->id())
+            ->paginate(12);
+
+        return response()->json([
+            'status' => true,
+            'data'   => $offers->items(),
+            'meta'   => [
+                'total'        => $offers->total(),
+                'per_page'     => $offers->perPage(),
+                'current_page' => $offers->currentPage(),
+                'last_page'    => $offers->lastPage(),
+            ],
+        ]);
+    }
+
+    public function show(int $id)
+    {
+        $offer = DivingOffer::find($id);
+
+        if (!$offer) {
+            return response()->json(['status' => false, 'message' => '課程不存在'], 404);
+        }
+
+        if ($offer->provider_id !== auth()->id()) {
+            return response()->json(['status' => false, 'message' => '無權限查看此課程'], 403);
+        }
+
+        return response()->json(['status' => true, 'data' => $offer]);
+    }
+
+    public function store(Request $request)
+    {
+        $validated = $request->validate([
+            'title'       => 'required|string|max:255',
+            'location'    => 'required|string|max:255',
+            'spot'        => 'nullable|string|max:255',
+            'price'       => 'required|integer|min:0',
+            'region'      => 'required|string|max:100',
+            'tag'         => 'nullable|string|max:100',
+            'badges'      => 'nullable|array',
+            'badges.*'    => 'string|max:50',
+            'description' => 'nullable|string',
+        ]);
+
+        $validated['provider_id'] = auth()->id();
+        $validated['rating']      = 0;
+        $validated['reviews']     = 0;
+
+        $offer = DivingOffer::create($validated);
+
+        return response()->json(['status' => true, 'data' => $offer], 201);
+    }
+
+    public function update(Request $request, int $id)
+    {
+        $offer = DivingOffer::find($id);
+
+        if (!$offer) {
+            return response()->json(['status' => false, 'message' => '課程不存在'], 404);
+        }
+
+        if ($offer->provider_id !== auth()->id()) {
+            return response()->json(['status' => false, 'message' => '無權限修改此課程'], 403);
+        }
+
+        $validated = $request->validate([
+            'title'       => 'nullable|string|max:255',
+            'location'    => 'nullable|string|max:255',
+            'spot'        => 'nullable|string|max:255',
+            'price'       => 'nullable|integer|min:0',
+            'region'      => 'nullable|string|max:100',
+            'tag'         => 'nullable|string|max:100',
+            'badges'      => 'nullable|array',
+            'badges.*'    => 'string|max:50',
+            'description' => 'nullable|string',
+        ]);
+
+        $offer->fill($validated)->save();
+
+        return response()->json(['status' => true, 'data' => $offer]);
+    }
+
+    public function destroy(int $id)
+    {
+        $offer = DivingOffer::find($id);
+
+        if (!$offer) {
+            return response()->json(['status' => false, 'message' => '課程不存在'], 404);
+        }
+
+        if ($offer->provider_id !== auth()->id()) {
+            return response()->json(['status' => false, 'message' => '無權限刪除此課程'], 403);
+        }
+
+        $offer->delete();
+
+        return response()->json(['status' => true, 'message' => '課程已刪除']);
+    }
+}

app/Models/DivingOffer.php

@@ -11,6 +11,7 @@ class DivingOffer extends Model
     protected $table = 'diving_offers';
 
     protected $fillable = [
+        'provider_id',
         'title',
         'location',
         'spot',