Add VERSIONING.md, ROADMAP.md, and DEPENDENCY_POLICY.md

[felixweinberger]

Add standalone policy/governance files to match the TypeScript SDK's structure (PR #1547). These files are checked by the tier-check CLI.

Motivation and Context

The tier-check CLI checks for specific file paths (VERSIONING.md, ROADMAP.md, DEPENDENCY_POLICY.md, .github/dependabot.yml). The Python SDK already had dependabot.yml and dependency/triage policy content in CONTRIBUTING.md, but was missing the standalone files.

How Has This Been Tested?

Manual review. These are documentation-only files.

With the tier-check skill:

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

Adapted from TypeScript SDK PR #1547 with Python-specific changes:

• VERSIONING.md: DeprecationWarning instead of JSDoc @deprecated, Python version support instead of Node.js LTS
• ROADMAP.md: identical content (shared spec tracking and v2 milestones across SDKs)
• DEPENDENCY_POLICY.md: references weekly uv lock --upgrade workflow, compatible-release specifiers (~=) instead of caret ranges (^), uv.lock for reproducibility
• CONTRIBUTING.md: updated to link to standalone DEPENDENCY_POLICY.md

[maxisbey]

Manual review. These are documentation-only files.

@felixweinberger there are a lot of source code changes in this pr, are they meant to be there?

[felixweinberger]

Manual review. These are documentation-only files.

@felixweinberger there are a lot of source code changes in this pr, are they meant to be there?

pleasures of dealing with main and v1.x not sure what happened here fixing.