feat(upkuajing): add B2B research MCP plugin

[Upkuajing]

What / 改动内容

Add UpKuaJing (跨境魔方), version 1.0.5, in the productivity category. The plugin connects to the hosted HTTP MCP service at https://mcp.upkuajing.com/mcp and includes a skill for B2B company/contact discovery, trade research, lead enrichment and explicitly requested outreach.

Includes English/Chinese README documentation and marketplace descriptions, localized display names, a logo, and an MIT license for the configuration, documentation and skill. No local executable scripts, hooks or server source are bundled. An UpKuaJing account and OAuth authorization are required. Paid actions require live pricing and explicit cost confirmation; message delivery additionally requires approval of recipients and content.

Verification and outstanding runtime checks

• Official validator and distribution build pass locally.
• Local installation, enablement, Chinese display name and logo display were confirmed in ZCode.
• On September 14, 2026, the maintainer confirmed successful production OAuth login and account balance retrieval in ZCode after the authorization service callback-encoding fix. This runtime result was reported by the maintainer; the submitting agent did not independently observe that session.
• Token refresh remains unverified.
• Business-result rendering remains unverified. No paid queries or message delivery were performed.

Ready for review. The earlier OAuth callback failure is resolved in the maintainer's production ZCode test. The packaged README verification notes describe the earlier packaging-stage checks; this PR records the subsequent successful login and balance lookup.

Self-check / 自查清单

• Plugin name is unique kebab-case; directory is plugins/upkuajing/.
• Version is synchronized as 1.0.5 in plugin.json and marketplace.json.
• English and Chinese README files are equivalent.
• description_i18n includes en and zh-CN.
• No secrets, machine-specific paths or private dependencies are included.
• Model/API/network dependencies and side effects are documented.
• python3 scripts/validate.py and python3 scripts/build_dist.py pass locally.