feat(docs): document generic interface generate() and update examples

[DiogoRibeiro7]

• Add usage example for generate(model="...") in index.md
• Include interface module in API reference via modules.md
• Ensure Sphinx rebuild shows new interface in rendered docs

[Copilot]

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• docs/source/gen_surv.rst: Language not supported

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gen_surv/interface.py	90.00%	1 Missing ⚠️

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