feat: add Translate text button backed by translator microservice

[anthony-tom1]

Context

This PR adds a new “Translate text” action under each topic post so users can request English translation on demand. It introduces end-to-end wiring from the post UI to a new NodeBB API endpoint, and from that endpoint to the external translator microservice with safe fallback behavior.

Summary

• Added “Translate text” button and translation result panel under each post’s content in Harmony post templates
• Added frontend click handling on topic posts to:
  • call GET /api/v3/posts/:pid/translate
  • show loading/detected-language/translated text states
  • gracefully handle failures
• Added new backend API endpoint GET /api/v3/posts/:pid/translate
• Integrated server-side translation call to external microservice:
  • GET ${TRANSLATOR_URL}/?content=<urlencoded text>
  • configurable timeout via LLM_TRANSLATE_TIMEOUT_MS (default 5000)
  • fallback to original text when service is unavailable
• Added i18n labels/messages for translation UI (en-US, en-GB, en-x-pirate)

Files Changed

• vendor/nodebb-theme-harmony-main/templates/partials/topic/post.tpl: add translate button + translation container
• vendor/nodebb-theme-harmony-2.1.35/templates/partials/topic/post.tpl: add translate button + translation container
• public/src/client/topic/postTools.js: add post translate click handler and UI update logic
• src/routes/write/posts.js: add GET /:pid/translate route
• src/controllers/write/posts.js: add Posts.getTranslation controller
• src/api/posts.js: implement postsAPI.getTranslation with microservice call + timeout + fallback
• public/language/en-US/search.json: add translation UI strings
• public/language/en-GB/search.json: add translation UI strings
• public/language/en-x-pirate/search.json: add translation UI strings

Testing

• Lint check on changed backend/frontend files: no linter errors reported
• Manual code-path verification:
  • button markup exists in both Harmony post templates
  • frontend event handler exists for [component="post/translate"]
  • route/controller/api wiring exists for /:pid/translate
• Note: full runtime manual test requires local Redis + NodeBB startup

Manual Verification Steps

1. Set translator service URL (if not default): TRANSLATOR_URL=http://localhost:5001
2. Start Redis and NodeBB, then open a topic page
3. Click Translate text under a post
4. Confirm:
   • loading message appears
   • detected language label appears
   • translated English text (or fallback original text on service failure)