feat(core): 补全剩余 6 个 StreamField Block (ProductCard/Pricing/Timeline/Team/TechStack/Video)

- apps/core/blocks.py 新增 ProductCardBlock/PricingBlock/TimelineBlock/TeamBlock/TechStackBlock/VideoBlock，COMMON_BLOCKS 扩充至 14 个内容 Block
- TeamBlock 新增 TeamMemberChooserBlock(SnippetChooserBlock)，复用 FormBlock 已有的 get_api_representation 展开模式，展开 TeamMember 完整字段（含 serialize_image 复用）
- 为 blog/cases/home/products/solutions 五个 Page 模型生成并应用 alter field body 迁移（StreamField block 定义变更会写入迁移 state）
- apps/core/tests.py 新增 TeamMemberChooserBlock 空值/展开单元测试，pytest 33 个用例全部通过
- 设计文档 §2.6/§2.16 同步更新为已实现

apps/core/tests.py

@@ -2,7 +2,7 @@
 import pytest
 from rest_framework.test import APIClient
 
-from apps.core.blocks import FormBlock
+from apps.core.blocks import FormBlock, TeamMemberChooserBlock
 from apps.core.models import (
     NavigationMenu,
     NavigationMenuItem,
@@ -159,6 +159,26 @@ def test_testimonial_api_returns_list():
     assert response.data["items"][0]["author_name"] == "客户A"
 
 
+def test_team_member_chooser_block_api_representation_expands_fields():
+    """TeamMemberChooserBlock.get_api_representation 应展开 TeamMember 的完整字段，
+    而不是仅返回 SnippetChooserBlock 默认的主键。"""
+    member = TeamMember.objects.create(name="王五", role="产品经理", bio="十年行业经验")
+
+    block = TeamMemberChooserBlock()
+    result = block.get_api_representation(member)
+
+    assert result["id"] == member.pk
+    assert result["name"] == "王五"
+    assert result["role"] == "产品经理"
+    assert result["bio"] == "十年行业经验"
+    assert result["photo"] is None
+
+
+def test_team_member_chooser_block_api_representation_handles_none():
+    block = TeamMemberChooserBlock()
+    assert block.get_api_representation(None) is None
+
+
 def test_partner_api_returns_list():
     Partner.objects.create(name="伙伴A", website_url="https://partner-a.example.com")