v0.4.0

Changes

• Add URL extraction mode via --extract (deprecated alias: --extract-only) with --format md|text.
• Rename HTML→Markdown conversion flag to --markdown-mode (deprecated alias: --markdown).
• Add --preprocess off|auto|always and a uvx markitdown fallback for Markdown extraction + unsupported file attachments (when --format md is used).
• When uvx isn’t available, print an install hint (brew install uv).

Tests

• Add coverage for preprocess + markitdown integration paths.