Add cursor pagination for list timelines

[RuochenLyu]

Summary

• add --cursor support to twitter list
• expose pagination.nextCursor for structured list timeline output
• thread cursor/return-cursor support through fetch_list_timeline
• document the list pagination workflow in README and SKILL.md

This follows the same shape as #49 for feed cursor pagination, reusing the existing timeline cursor extraction and structured pagination envelope.

Validation

• uv run pytest -q
• uv run mypy twitter_cli
• uv run ruff check .
• real list pagination smoke test with list 2049103846925029525: page 1 returned 5 tweets and a cursor; page 2 with that cursor returned 5 different tweets and a new cursor.

[jackwener]

Reviewed the list cursor pagination changes. No blocking findings. The implementation threads cursor/return_cursor through fetch_list_timeline, emits pagination.nextCursor for structured output, and has focused CLI/client tests. Local checks: ruff passed, mypy passed, new focused tests passed. Full pytest currently hits two pre-existing Rich table truncation assertions that also fail on main in this local env, so they are not introduced by this PR.