feat(mindspace): 公开页分享组件、workspace 路径与 Plaza 发布增强

- 新增 public share widget 与 workspace relative path 解析
- 增强 publications/chat-plaza 发布链路与缩略图 demo
- 补充 schema、cover 检查脚本与回归测试

Co-authored-by: Cursor <cursoragent@cursor.com>

mindspace-service/mindspace-rpc-server.test.mjs

@@ -47,6 +47,7 @@ function createStubAdapter() {
       async createPage() { return { ok: true }; },
       async deletePage() { return { ok: true }; },
       async findPageByRelativePath() { return null; },
+      async findPlazaContextByWorkspacePath() { return null; },
       async findPageBySourceAsset() { return null; },
       async getDeletePreview() { return { ok: true }; },
       async getPage() { return { ok: true }; },
@@ -74,6 +75,7 @@ function createStubAdapter() {
       async check() { return { ok: true }; },
       async cleanupExpiredUnconfirmedPublications() { return { cleaned: 0 }; },
       async getCurrent() { return null; },
+      async refreshOnlinePublicationHtml() { return null; },
       async getPublicHomepage() { return null; },
       async getStats() { return { ok: true }; },
       async offline() { return { ok: true }; },