v0.2.1 - skill-first positioning

Documentation and positioning release. No code changes.

• Lead with the reddit-poster Claude skill as the primary surface; CLI is the engine it drives, MCP is the optional transport.
• Reworked README: skill install moved up front, MCP demoted to optional, expanded "why this exists" (human-style posting + correct flair handling).
• Updated package description, keywords, and GitHub repo description to be skill-first.
• Completed the reddit-mcp to reddit-skill URL rename across pyproject and examples.