Add opt-in Xquik publishing backend

[kriptoburak]

Summary

• Add an opt-in Xquik backend through TWITTER_BACKEND=xquik.
• Preserve Tweepy as the default and accept the existing twitter alias.
• Read the Xquik API key and connected-account selector from the environment.
• Reuse the existing Twitter text cleanup for both publishing backends.
• Send a unique Idempotency-Key for every automatic Xquik post.
• Document setup and the current create-tweet API reference.
• Add focused regression tests for both publishing paths.

Why

The bot already routes TradingView alerts to several destinations, including Twitter through Tweepy. The Xquik backend adds an optional API-key path for connected X accounts without changing existing installations. A unique idempotency key is required by the current Xquik write contract and prevents accidental request replay within an API call.

Validation

• Installed the exact requirements.txt on Python 3.9.18
• python -m unittest discover -s tests -p 'test_*.py' -v (5 tests)
• black --check tests/test_handler.py
• flake8 --ignore E501 config.py handler.py tests/test_handler.py
• python -m py_compile config.py handler.py main.py tests/test_handler.py
• Public Xquik create-tweet contract and links
• Credential-literal scan
• git -c core.whitespace=cr-at-eol diff --check
• Clean rebuild on current master

The current PR is limited to the publishing integration. It does not change webhook proxy trust.

[github-actions]

It looks like this PR has been idle a while, so I am marking it as stale. Remove the label or comment if this is still being worked on.

[kriptoburak]

This PR remains active. Current head 2a0d9c4 supersedes the earlier scope and is rebuilt on current master.

The unrelated proxy-trust changes and MCP copy are removed. The focused integration now includes the required unique Idempotency-Key, preserves Tweepy by default, and adds 5 passing tests for configuration, request shape, text cleanup, and both backend routes.

[kriptoburak]

This contribution is still active. Current head 2a0d9c4c is mergeable/clean and includes the opt-in backend, README setup, and 5 focused regression tests. The documented Python 3.9 unit, Black, Flake8, compile, contract, secret-literal, and diff checks pass. Please remove the stale no-activity label when the automation rechecks it.