docs: mark linkedQueryParam as stable and expand documentation

- Updated badge from "experimental" to "stable."
- Expanded documentation with detailed examples:
  - Added "Quick Start" section for beginner-friendly usage.
  - Clarified the usage of built-in parsers (`paramToNumber`, `paramToBoolean`) with examples.
  - Added sections for handling null/undefined values, coalesced updates, and dynamic keys.
  - Provided examples for integration with input signals, writable signals, and model signals.
- Introduced best practices for efficient and maintainable usage.
- Revised outdated TODO comment and added missing references.

Author: eneajaho