Add optional Xquik search backend

[kriptoburak]

Summary

• add an optional SEARCH_BACKEND=xquik / hermes-tweet path for the search_tweets MCP tool
• keep retweet, like, post, and default Twitter search on the existing OAuth flow
• normalize Xquik/Hermes Tweet response shapes into the existing formatter and add timeout/error handling
• document the new environment variables and add Vitest coverage for the adapter and MCP branch

Validation

• npm ci --ignore-scripts --no-audit --no-fund
• npm run build
• npm run check-types
• npm test
• git diff --cached --check
• secret-pattern scan over tracked public text

Notes

• npm pack --dry-run --json is not available on current main because package.json has no name field; this PR does not change package metadata.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Honor Hermes API key when XQUIK key is blank

apiKey is selected with nullish coalescing, so an empty XQUIK_API_KEY (common when .env contains XQUIK_API_KEY=) wins over a populated HERMES_TWEET_API_KEY. In that configuration, searchTweetsWithXquik receives "", fails the trim check, and every search_tweets call errors even though the alternate key is set as documented. Use a fallback that treats blank strings as missing (e.g., trim before choosing, or use a non-empty check) so the Hermes key path actually works.

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