docs: add FTS docs

[prrao87]

We lack docs for how to create and query an FTS index in Lance. This PR adds detailed docs, based on the latest v1.0.4 pylance API. All code snippets have been tested with the latest stable release and I gave it another pass with GPT 5.2 to ensure accuracy per the latest Rust code in tokenizer.rs.

[github-actions]

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[github-actions]

PR Review: docs: add FTS docs

Good documentation addition covering FTS capabilities in Lance. The content is well-organized and the code examples are consistent with the current Python API.

P1: Documentation Link Error

In docs/src/quickstart/vector-search.md, the "Next Steps" section links to the wrong file:

Check out **[Full-text Search](../quickstart/versioning.md)**, where we show...

This should link to full-text-search.md, not versioning.md:

Check out **[Full-text Search](../quickstart/full-text-search.md)**, where we show...

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The API examples appear accurate based on current implementation in python/python/lance/dataset.py and python/python/lance/query.py.