fittok v0.3.1

Docs-accuracy release. No code/behavior change from 0.3.0.

• All install/usage docs unified on uv/uvx (one tool for MCP + CLI; uv add for the library).
• Added clear 'how to add the MCP' steps (claude mcp add fittok -- uvx fittok + /mcp verify).
• Fixed README env-var names to the real FITTOK_* (were stale CONTEXT_OPTIMIZER_*).

📦 https://pypi.org/project/fittok/0.3.1/