feat(pricewin): add live hotel and flight price comparison plugin - #61

Summary

Add PriceWin 1.0.5 to the utilities category, as a community plugin under
external_plugins/pricewin. The plugin connects ZCode to
PriceWin's hosted MCP server, which compares live hotel and flight prices
across Booking.com, Agoda, Trip.com and Traveloka, in USD.

Includes one remote HTTP MCP declaration (https://mcp.price.win/mcp, no
OAuth, no API key), one Skill (pricewin-travel-search), English and Chinese
READMEs, a marketplace entry and a 256×256 icon under assets/pricewin/. No
local server, executable, install script or hook is bundled.

Access and side effects

• Tool arguments (city, dates, party size, hotel name, airports, cabin) go to
  mcp.price.win, plus a short excerpt of the request used only to choose the
  reply language.
• request_booking sends the guest's name, phone and email to a partner hotel
  through OpenTravel (api.travelopen.ai, same developer). It takes no
  payment and holds no room. Cancelling needs a single-use token emailed to the
  booking address.
• Prices are read from the OTAs' public pages at search time; there is no
  partnership with those sites, and each result links to its source.
• No local file reads or writes, no commands.

All of this is in the plugin README.

License

Manifest, Skill and docs are MIT. The PriceWin service, name and icon are
provided by PriceWin and not licensed by this plugin. The same files are
maintained upstream at https://github.com/PriceDotWin/pricewin-agent-plugin.

Validation

• Rebased onto current main as one commit. python3 scripts/validate.py: OK,
  47 plugins; tests/test_catalog_classification.py, tests/test_tree_safety.py
  and tests/test_icon_assets.py: 25 passed; git diff --check clean.
• The identical MCP declaration and Skill were installed and exercised in
  Claude Code, Codex CLI and Antigravity: install, tool discovery,
  search_hotels_live → poll_search_results returned live prices (e.g. Da
  Nang, 2 adults, Nov 10–12), and search_flights_live returned fares.
• I don't have a macOS/Windows machine with ZCode at hand, so the ZCode GUI
  run is not done yet. I will add the steps and a screenshot here once it is.

Self-check / 自查清单

• Unique kebab-case plugin name and matching directory.
• Version 1.0.2 matches in manifest and marketplace (same as upstream).
• English and Chinese READMEs are equivalent.
• Localized descriptions include en and zh-CN.
• No secrets, machine-specific paths, or private dependencies.
• Network dependencies and side effects are documented.
• Repository validation and distribution package pass locally.