feat: add sendTweet with media upload support

[Faareoh]

⚠️ This PR was entirely generated by Claude (claude-sonnet-4-6), inspired by
the reference implementation at https://github.com/0x4337/agent-twitter-client-grokky.

Summary

• src/api-data.ts — adds mutationEndpoints.CreateTweet (current queryId + x.com URL)
• src/tweets.ts — implements uploadMedia() (chunked video + simple image) and sendTweet() returning Tweet | null
• src/scraper.ts — exposes sendTweet() as a public method on the Scraper class
• src/_module.ts — exports the new MediaData type
• src/tweet-mutations.test.ts — unit tests + opt-in integration tests for the mutation

Key details

• Uses the CreateTweet GraphQL mutation (queryId: S1qcGUn68_U0lDKdMlYSGg) via POST x.com/i/api/graphql/…
• Injects __typename: 'Tweet' on the response when absent (the CreateTweet API omits it) so the existing parser can handle it
• Generates x-client-transaction-id when the experimental.xClientTransactionId option is enabled, to avoid Twitter's 226 "looks automated" errors
• MediaData accepts { data: Buffer, mediaType: string }; videos use the chunked INIT/APPEND/FINALIZE flow with status polling

Test plan

• npm test — all unit tests pass
• Integration tests run with real credentials: set TWITTER_* env vars and run npx jest tweet-mutations --testNamePattern=integration

[Morad37]

The sendTweet function and its integration with media upload is a solid addition. One area that could use hardening: the media/upload step's error response is not shown being validated in the available diff. If X returns a non-JSON response or a response missing media_id_string, the downstream code would attempt to use undefined as the media ID, which would likely produce a confusing API error from the CreateTweet endpoint. Consider validating that the upload response contains a valid string media_id_string before continuing to the tweet mutation, and returning a clear error if it doesn't. The test mock always returns { media_id_string: 'mock_media_id' }, which is fine for happy-path coverage but means an upload failure would not be exercised. A test case with a mock that returns an error from media/upload would fill that gap.