docs: add pre-commit setup to bootstrap and deduplicate contributing guides

[bearomorphism]

Description

Add missing pre-commit hook installation instructions and deduplicate the three contributor-facing docs (AGENTS.md, contributing.md, contributing_tldr.md).

• Add uv run poe setup-pre-commit step to AGENTS.md bootstrap
• Clarify what prek is with a link to its repository
• Add cross-references between AGENTS.md and contributing.md
• Refactor contributing_tldr.md into a pure command cheat sheet, removing duplicated prerequisites/setup already in contributing.md
• Fix bare mypy/pytest commands to use uv run prefix
• Fix anchor link to prerequisites section

Checklist

• I have read the contributing guidelines

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: GitHub Copilot following the guidelines

Code Changes

• Add test cases to all the changes you introduce (docs-only change)
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • Ensure backward compatibility is maintained
  • Document any manual testing steps performed
• Update the documentation for the changes

Documentation Changes

• Run uv run poe doc locally to ensure the documentation pages renders correctly
• Check and fix any broken links (internal or external)

Expected Behavior

All three docs cross-reference contributing.md as the single source of truth for prerequisites and setup. No duplicated content across files.

Steps to Test This Pull Request

1. Run uv run mkdocs build --strict — should build with no broken link warnings
2. Review AGENTS.md bootstrap section — should include setup-pre-commit
3. Review contributing_tldr.md — should be a concise command cheat sheet with a pointer to contributing.md

Additional Context

The prek link was initially pointing to commitizen-tools/prek (404); corrected to j178/prek.