Add link-checker agentic workflow for automated documentation maintenance (#158)

* Initial plan

* Add link-checker agentic workflow

Create automated workflow to check and fix broken links in documentation:
- Runs daily on weekdays
- Pre-step collects and tests all links using scripting
- Uses cache memory to track unfixable broken links
- Creates PRs with fixed URLs when needed
- Uses web-fetch for finding alternative URLs

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Add documentation for link-checker workflow

Create comprehensive documentation for the new link checker workflow and add it to the README

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* Fix documentation inconsistency in link-checker

Update docs to correctly state that PRs are created as ready-to-review (non-draft)

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: Peli de Halleux <pelikhan@users.noreply.github.com>

Author: Copilot