Add lychee local link checker

[josecelano]

Summary

Add deterministic local Markdown link and fragment validation to the shared linter CLI.

• Adds linter lychee and includes it in linter all.
• Runs Lychee with --offline, discovers lychee.toml, and checks **/*.md plus .github/**/*.md while excluding generated target/ content.
• Installs missing Lychee through cargo install lychee.
• Documents the linter and captures local-link failure verification evidence.
• Repairs stale local links in existing feature documentation in a separate commit.

Validation

• cargo run

Closes #3

[Copilot]

🟡 Changes recommended

The new lychee runner and verification docs have a couple of reproducible, user-visible rough edges (noisy .github glob warnings and a non-reproducible verification invocation) that should be addressed before approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds a new lychee subcommand to the torrust-linting CLI to perform deterministic, offline validation of local Markdown links/fragments, and wires it into the standard linter all workflow while updating docs to reflect the new capability.

Changes:

• Introduces a new Lychee linter runner (run_lychee_linter) with auto-install via Cargo and offline execution over Markdown files.
• Adds linter lychee subcommand and includes it in run_all_linters().
• Updates README and internal issue/feature documentation (including link repairs and verification notes).

File summaries

File	Description
src/linters/mod.rs	Registers and re-exports the new lychee linter module.
src/linters/lychee.rs	Implements Lychee install + offline link/fragment checking runner.
src/cli.rs	Adds Lychee subcommand and runs it as part of all.
README.md	Documents the new linter, command usage, tool install, and lychee.toml discovery.
project-words.txt	Adds mktemp to spell-check allowlist for new docs content.
docs/issues/3-add-lychee-local-markdown-link-checker/verification.md	Adds manual verification evidence for offline failure behavior.
docs/issues/3-add-lychee-local-markdown-link-checker/questions.md	Records design decisions for the Lychee linter integration.
docs/issues/3-add-lychee-local-markdown-link-checker/ISSUE.md	Adds the issue spec/plan/acceptance criteria for the Lychee feature.
docs/features/linter-parallel-execution/specification.md	Updates related-doc links and reorganizes resource references.
docs/features/linter-parallel-execution/questions.md	Updates related-doc links and reorganizes resource references.
docs/features/linter-auto-fix/specification.md	Updates related-doc links and reorganizes resource references.
docs/features/linter-auto-fix/README.md	Cleans up headings and updates related-doc/resource links.

Review details

• Files reviewed: 12/12 changed files
• Comments generated: 2
• Review effort level: Lite

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[josecelano]

ACK 5da34af