Docs: Create Self-Explanatory Tools via OpenAPI Descriptions

This ticket is a sub-task of the epic #7604.

To reduce the complexity of AGENTS.md, we will move detailed tool documentation directly into the tool descriptions themselves within the OpenAPI specifications. This will make the tools "self-explanatory".

Vision:

The openapi.yaml file for each MCP server should become the single source of truth for how to use its tools. An agent should be able to learn how to use a tool just by reading its description.

Requirements for each tool's description:

1. A clear summary of what the tool does.
2. A "When to Use" section with specific scenarios.
3. Detailed examples of how to call the tool, including parameters.
4. Clear explanations of the tool's output.

AGENTS.md will then be refactored into a higher-level document that directs agents to explore the tools and their embedded documentation.

Acceptance Criteria:

1. Review and update the openapi.yaml for all three MCP servers (knowledge-base, memory-core, github-workflow).
2. Ensure the description for every tool is comprehensive enough to not require external documentation.
3. Add rich, practical examples to the descriptions.