Add optional Xquik posting backend

[kriptoburak]

Summary

• Add opt-in TWITTER_BACKEND=xquik support for posting through Xquik.
• Keep the existing X API v2 OAuth 1.0a path as the default.
• Send account and text to POST /api/v1/x/tweets.

Independent Repository Fixes

• Make the documented shell environment configuration work for the existing X API backend.
• Return a nonzero process status when an API returns an unsuccessful HTTP response.
• Avoid the PHP 8.5 curl_close() deprecation while retaining PHP 7 compatibility.

Configuration

Set TWITTER_BACKEND=xquik, XQUIK_API_KEY, and XQUIK_ACCOUNT. XQUIK_API_BASE is optional and defaults to https://xquik.com/api/v1.

Validation

• php -l config.php
• php -l post_tweet.php
• Local request-contract fixture verified method, route, x-api-key, account, text, success parsing, and exit status.
• Unreachable endpoint fixture verified cURL failures return status 1 without PHP warnings.
• git diff --check
• Xquik API root returned 200.
• Protected tweet route returned 401 without credentials.

Xquik is an independent third-party service. Not affiliated with X Corp.
"Twitter" and "X" are trademarks of X Corp.

[kriptoburak]

Rebuilt this pull request on the current main branch as 1 verified signed commit.

The revised diff keeps the Xquik backend focused and preserves the existing X API flow. It also fixes 3 independent repository issues:

• Shell environment variables now work for the existing X API credentials as documented.
• Unsuccessful HTTP responses now return a nonzero process status.
• PHP 8.5 no longer emits the curl_close() deprecation while PHP 7 remains supported.

Validation completed:

• Both PHP files pass php -l.
• A local request fixture verified the Xquik method, route, header, payload, response parsing, and success status.
• An unreachable endpoint fixture verified cURL failures return status 1 without warnings.
• The live API root returns 200, and the protected tweet route returns 401 without credentials.
• git diff --check passes.

No review comments, review threads, or check failures are outstanding.