[fnayou]

Summary

 docs-quality PR workflow
+  strict Zensical build on every PR to main
+  local link and generated-page accessibility checks
+  `task docs:check` for the same local gate

Adds a standard-library checker and unit tests, CI workflow, local task, and contributor instructions. The Pages deploy workflow remains main-only with its existing permissions.

Closes #34

Evidence

• Before: documentation had no PR build or quality check.
• After: task docs:check passed; 8 checker tests passed; strict build and checks passed for 8 generated pages.

Merge Danger

Door: Two-way

Blast Radius: Docs

Revert the PR to remove the checker, CI workflow, task, and contributor instructions.