v0.7.0: pastes of any language

A paste is now whatever was pasted. JSON, JavaScript, TypeScript, Python, shell, YAML, HTML, CSS, SQL, Go, Rust, Java, C, Dockerfiles, diffs and some thirty languages in all render on readm3.com as highlighted, numbered, foldable code in the reader's theme; Markdown still renders as a document. The language is detected from the file name's extension when it has one and from the content otherwise, and can be forced with --language. Every paste page has Copy, Raw (/p//raw, always plain text; ?download=1 for the file with its own type) and Download. Minified JSON is shown pretty-printed. readm3 paste FILE now sends the file name so the extension decides; the paste_create MCP tool takes language. PR #12.