docs: update options documentation and fix broken links (Closes #3117)

[Aster1145]

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[github-actions]

No generated-output differences

✅ This PR does not change generated outputs.

[schani]

Thank you for your PR!

The broken-link fixes are useful, so I extracted them into the smaller, focused #3158. That PR credits you as a co-author.

The options guide needs a few accuracy corrections before it can be merged:

• Most entries presented as JS/TS properties are not part of the public quicktype-core Options type. topLevel, srcLang, srcUrls, additionalSchema, the GraphQL/HTTP fields, telemetry, quiet, buildMarkovChain, help, and version are internal CLI options. In particular, inputData must be an InputData instance rather than a filename, URL, or directory.
• --dense / rendererOptions["dense"] and --pad-empty-lines / rendererOptions["pad-empty-lines"] do not exist. The density option supported by C#, Swift, and Rust is --density normal|dense, mapped to rendererOptions["density"].
• The documented acronym value lower-case is invalid; the actual value is lowerCase.
• CLI --out can participate in inferring the language and top-level name, but the programmatic outputFilename property itself does not perform that inference.
• README calls this a “full mapping,” but the guide includes only five of the many language-specific renderer options and does not map the app's option labels to CLI/API options, which is a central part of [FEATURE]: document options #3117. For that reason, this does not yet fully close the issue.
• The introduction says all --no-* flags disable inference behavior, but --no-ignore-json-refs is the exception: it enables JSON $ref handling by setting ignoreJsonRefs to false.

I think the guide would be clearest if it separated direct public-API mappings, input-construction recipes, CLI-only options, and per-language renderer options.