docs: add MAINTAINERS.md to document project maintainers

Feature description

Add a root-level MAINTAINERS.md that lists the current PowerContext maintainers and links to their GitHub profiles, following the example of MCP's MAINTAINERS.md.

Problem and proposed solution

The repository currently has no root-level maintainer list. A clearly documented list would help users and contributors understand who maintains the project and whom to involve in reviews, technical discussions, and project-level decisions.

Suggested contents:

• Each current maintainer's name and GitHub profile link.
• A brief description of maintainer responsibilities, with ownership areas where applicable.
• Separate lead/core or component maintainer sections only if those roles already exist in PowerContext.
• A last-updated date and a short note on how the list is kept current.

The project team should confirm the initial roster and roles. Commit activity alone should not be used to infer maintainer status.

Link the document from the README and CONTRIBUTING.md so that new contributors can find it easily. Keep the structure lightweight and appropriate to the project's current team size.

Alternatives considered

GitHub's contributors page shows contribution history but does not establish current maintainer responsibilities. CODEOWNERS can help route reviews, but a dedicated maintainer document provides a more accessible overview of project ownership.

Additional context

The MCP document provides a useful example of listing maintainers by role or project area with links to their GitHub profiles. PowerContext can adopt the relevant parts without introducing additional governance roles solely to match that structure.

Review the MCP MAINTAINERS.md example, then inspect the README and CONTRIBUTING.md to determine where the new document should be linked. Ask the project team to confirm the current maintainer roster, roles, and ownership areas rather than inferring them from commit activity. Done means a root-level MAINTAINERS.md has confirmed profile links, responsibilities, a last-updated date, maintenance guidance, and links from both documents.