移除官网展示用 Agent 目录 (#109)

## 变更

- 移除此前为官网展示加入的 7 个 Agent 条目
- 恢复 Market 为真实可复用目录，不再承载官网宣传样例
- 恢复 README 与 manifest 中的 Agent 计数

## 验证

- `scripts/i18n/test_validate_i18n.py`
- `scripts/catalog/test_validate_catalog_metadata.py`
- `scripts/catalog/test_collection_generator.py`
- `scripts/catalog/validate_catalog_metadata.py --require-complete`
- `scripts/i18n/validate-i18n.py`
- 敏感信息与发布边界检查通过

README.md

@@ -10,7 +10,7 @@ DesireCore 官方市场仓库，存放官方维护的 Agent/Skill 定义，以
 ├── categories.json        # Category registry and localized labels
 ├── builtin-skills.json    # Built-in local SKILL.md skills
 ├── agents/
-│   └── <agent-id>/
+│   └── desirecore/
 │       └── agent.json
 └── skills/
     ├── <local-skill>/
@@ -22,9 +22,7 @@ DesireCore 官方市场仓库，存放官方维护的 Agent/Skill 定义，以
 
 The market currently contains:
 
-- `8` Agents: `desirecore`, `content-marketing-agent`, `tender-collaboration-agent`,
-  `contract-review-agent`, `engineering-drawing-review-agent`, `inspection-report-agent`,
-  `research-evidence-agent`, `workflow-operations-agent`
+- `1` Agent: `desirecore`
 - `34` local built-in skills with `SKILL.md`
 - `28` external skill entries with `entry.json`
 - `62` publishable skills in total (`SKILL.md` + `entry.json`)