docs: improve contribution workflow and project governance (#246)

* chore: bump esperanto for anthropic on langchain

* docs: improve contribution workflow and project governance

Implements a comprehensive contribution management system to maintain project quality and vision while welcoming community contributions.

Key Changes:
- Updated CONTRIBUTING.md with clear issue-first workflow
- Added "willing to contribute" checkbox to issue templates
- Created DESIGN_PRINCIPLES.md documenting project vision and principles
- Added comprehensive PR template with quality checklists
- Created MAINTAINER_GUIDE.md with review processes and templates
- Added .github/README.md explaining the contribution flow

Benefits:
- Prevents wasted effort on misaligned contributions
- Maintains architectural consistency
- Provides clear expectations for contributors
- Gives maintainers tools to manage contributions effectively
- Educates contributors on project goals and standards

Related to managing increased community contributions while maintaining project direction.

.github/pull_request_template.md

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+## Description
+
+<!-- Provide a clear and concise description of what this PR does -->
+
+## Related Issue
+
+<!-- This PR should be linked to an approved issue. If not, please create an issue first. -->
+
+Fixes #<!-- issue number -->
+
+## Type of Change
+
+<!-- Mark the relevant option with an "x" -->
+
+- [ ] Bug fix (non-breaking change that fixes an issue)
+- [ ] New feature (non-breaking change that adds functionality)
+- [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
+- [ ] Documentation update
+- [ ] Code refactoring (no functional changes)
+- [ ] Performance improvement
+- [ ] Test coverage improvement
+
+## How Has This Been Tested?
+
+<!-- Describe the tests you ran and/or how you verified your changes work -->
+
+- [ ] Tested locally with Docker
+- [ ] Tested locally with development setup
+- [ ] Added new unit tests
+- [ ] Existing tests pass (`uv run pytest`)
+- [ ] Manual testing performed (describe below)
+
+**Test Details:**
+<!-- Describe your testing approach -->
+
+## Design Alignment
+
+<!-- This section helps ensure your PR aligns with our project vision -->
+
+**Which design principles does this PR support?** (See [DESIGN_PRINCIPLES.md](../DESIGN_PRINCIPLES.md))
+
+- [ ] Privacy First
+- [ ] Simplicity Over Features
+- [ ] API-First Architecture
+- [ ] Multi-Provider Flexibility
+- [ ] Extensibility Through Standards
+- [ ] Async-First for Performance
+
+**Explanation:**
+<!-- Brief explanation of how your changes align with these principles -->
+
+## Checklist
+
+<!-- Mark completed items with an "x" -->
+
+### Code Quality
+- [ ] My code follows PEP 8 style guidelines (Python)
+- [ ] My code follows TypeScript best practices (Frontend)
+- [ ] I have added type hints to my code (Python)
+- [ ] I have added JSDoc comments where appropriate (TypeScript)
+- [ ] I have performed a self-review of my code
+- [ ] I have commented my code, particularly in hard-to-understand areas
+- [ ] My changes generate no new warnings or errors
+
+### Testing
+- [ ] I have added tests that prove my fix is effective or that my feature works
+- [ ] New and existing unit tests pass locally with my changes
+- [ ] I ran linting: `make ruff` or `ruff check . --fix`
+- [ ] I ran type checking: `make lint` or `uv run python -m mypy .`
+
+### Documentation
+- [ ] I have updated the relevant documentation in `/docs` (if applicable)
+- [ ] I have added/updated docstrings for new/modified functions
+- [ ] I have updated the API documentation (if API changes were made)
+- [ ] I have added comments to complex logic
+
+### Database Changes
+- [ ] I have created migration scripts for any database schema changes (in `/migrations`)
+- [ ] Migration includes both up and down scripts
+- [ ] Migration has been tested locally
+
+### Breaking Changes
+- [ ] This PR includes breaking changes
+- [ ] I have documented the migration path for users
+- [ ] I have updated MIGRATION.md (if applicable)
+
+## Screenshots (if applicable)
+
+<!-- Add screenshots for UI changes -->
+
+## Additional Context
+
+<!-- Add any other context about the PR here -->
+
+## Pre-Submission Verification
+
+Before submitting, please verify:
+
+- [ ] I have read [CONTRIBUTING.md](../CONTRIBUTING.md)
+- [ ] I have read [DESIGN_PRINCIPLES.md](../DESIGN_PRINCIPLES.md)
+- [ ] This PR addresses an approved issue that was assigned to me
+- [ ] I have not included unrelated changes in this PR
+- [ ] My PR title follows conventional commits format (e.g., "feat: add user authentication")
+
+---
+
+**Thank you for contributing to Open Notebook!** 🎉