Add PDF Mavericks Formatter to Online tools

[arunroyjhs]

Adds a client-side formatter to the Online tools section.

* [PDF Mavericks Formatter](https://www.pdfmavericks.com/json-formatter) - Formatter, validator and minifier with a tree view and JSONPath finder. Auto-repairs trailing commas and unquoted keys. Fully client-side, no signup.

Every feature named in the description is in the shipped page — tree view, JSONPath finder, auto-repair of trailing commas and unquoted keys, and minify. Parsing runs entirely in the browser: there are no fetch, axios or XMLHttpRequest calls anywhere in the tool's source, so pasted data never leaves the device.

Checked against CONTRIBUTING:

• Format matches * [project-name](url) - Description ends with a dot.
• Description does not describe the payload format, per the "it's implied" rule (JSONPath is kept as the query-language name)
• Searched the README for an existing entry — none
• No trailing whitespace
• Placed alongside the other fully client-side entries (JSON.fr, JSONtapose)